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PPPD(8) PPPD(8)
NAME
pppd - Point-to-Point Protocol Daemon
SYNOPSIS
pppd [ options ]
DESCRIPTION
PPP is the protocol used for establishing internet links over dial-up
modems, DSL connections, and many other types of point-to-point links.
The pppd daemon works together with the kernel PPP driver to establish
and maintain a PPP link with another system (called the peer) and to
negotiate Internet Protocol (IP) addresses for each end of the link.
Pppd can also authenticate the peer and/or supply authentication
information to the peer. PPP can be used with other network protocols
besides IP, but such use is becoming increasingly rare.
FREQUENTLY USED OPTIONS
ttyname
Use the serial port called ttyname to communicate with the
peer. The string "/dev/" is prepended to ttyname to form the
name of the device to open. If no device name is given, or if
the name of the terminal connected to the standard input is
given, pppd will use that terminal, and will not fork to put
itself in the background. A value for this option from a priv-
ileged source cannot be overridden by a non-privileged user.
speed An option that is a decimal number is taken as the desired baud
rate for the serial device. On systems such as 4.4BSD and
NetBSD, any speed can be specified. Other systems (e.g. Linux,
SunOS) only support the commonly-used baud rates.
asyncmap map
This option sets the Async-Control-Character-Map (ACCM) for
this end of the link. The ACCM is a set of 32 bits, one for
each of the ASCII control characters with values from 0 to 31,
where a 1 bit indicates that the corresponding control charac-
ter should not be used in PPP packets sent to this system. The
map is encoded as a hexadecimal number (without a leading 0x)
where the least significant bit (00000001) represents character
0 and the most significant bit (80000000) represents character
31. Pppd will ask the peer to send these characters as a
2-byte escape sequence. If multiple asyncmap options are
given, the values are ORed together. If no asyncmap option is
given, the default is zero, so pppd will ask the peer not to
escape any control characters. To escape transmitted charac-
ters, use the escape option.
auth Require the peer to authenticate itself before allowing network
packets to be sent or received. This option is the default if
the system has a default route. If neither this option nor the
noauth option is specified, pppd will only allow the peer to
use IP addresses to which the system does not already have a
route.
call name
Read options from the file /etc/ppp/peers/name. This file may
contain privileged options, such as noauth, even if pppd is not
being run by root. The name string may not begin with / or
include .. as a pathname component. The format of the options
file is described below.
connect script
Usually there is something which needs to be done to prepare
the link before the PPP protocol can be started; for instance,
with a dial-up modem, commands need to be sent to the modem to
dial the appropriate phone number. This option specifies an
command for pppd to execute (by passing it to a shell) before
attempting to start PPP negotiation. The chat (8) program is
often useful here, as it provides a way to send arbitrary
strings to a modem and respond to received characters. A value
for this option from a privileged source cannot be overridden
by a non-privileged user.
crtscts
Specifies that pppd should set the serial port to use hardware
flow control using the RTS and CTS signals in the RS-232 inter-
face. If neither the crtscts, the nocrtscts, the cdtrcts nor
the nocdtrcts option is given, the hardware flow control set-
ting for the serial port is left unchanged. Some serial ports
(such as Macintosh serial ports) lack a true RTS output. Such
serial ports use this mode to implement unidirectional flow
control. The serial port will suspend transmission when
requested by the modem (via CTS) but will be unable to request
the modem to stop sending to the computer. This mode retains
the ability to use DTR as a modem control line.
defaultroute
Add a default route to the system routing tables, using the
peer as the gateway, when IPCP negotiation is successfully com-
pleted. This entry is removed when the PPP connection is bro-
ken. This option is privileged if the nodefaultroute option
has been specified.
disconnect script
Execute the command specified by script, by passing it to a
shell, after pppd has terminated the link. This command could,
for example, issue commands to the modem to cause it to hang up
if hardware modem control signals were not available. The dis-
connect script is not run if the modem has already hung up. A
value for this option from a privileged source cannot be over-
ridden by a non-privileged user.
escape xx,yy,...
Specifies that certain characters should be escaped on trans-
mission (regardless of whether the peer requests them to be
escaped with its async control character map). The characters
to be escaped are specified as a list of hex numbers separated
by commas. Note that almost any character can be specified for
the escape option, unlike the asyncmap option which only allows
control characters to be specified. The characters which may
not be escaped are those with hex values 0x20 - 0x3f or 0x5e.
file name
Read options from file name (the format is described below).
The file must be readable by the user who has invoked pppd.
init script
Execute the command specified by script, by passing it to a
shell, to initialize the serial line. This script would typi-
cally use the chat(8) program to configure the modem to enable
auto answer. A value for this option from a privileged source
cannot be overridden by a non-privileged user.
lock Specifies that pppd should create a UUCP-style lock file for
the serial device to ensure exclusive access to the device.
mru n Set the MRU [Maximum Receive Unit] value to n. Pppd will ask
the peer to send packets of no more than n bytes. The value of
n must be between 128 and 16384; the default is 1500. A value
of 296 works well on very slow links (40 bytes for TCP/IP
header + 256 bytes of data). Note that for the IPv6 protocol,
the MRU must be at least 1280.
mtu n Set the MTU [Maximum Transmit Unit] value to n. Unless the
peer requests a smaller value via MRU negotiation, pppd will
request that the kernel networking code send data packets of no
more than n bytes through the PPP network interface. Note that
for the IPv6 protocol, the MTU must be at least 1280.
passive
Enables the "passive" option in the LCP. With this option,
pppd will attempt to initiate a connection; if no reply is
received from the peer, pppd will then just wait passively for
a valid LCP packet from the peer, instead of exiting, as it
would without this option.
OPTIONS
:
Set the local and/or remote interface IP addresses. Either one
may be omitted. The IP addresses can be specified with a host
name or in decimal dot notation (e.g. 150.234.56.78). The
default local address is the (first) IP address of the system
(unless the noipdefault option is given). The remote address
will be obtained from the peer if not specified in any option.
Thus, in simple cases, this option is not required. If a local
and/or remote IP address is specified with this option, pppd
will not accept a different value from the peer in the IPCP
negotiation, unless the ipcp-accept-local and/or ipcp-accept-
remote options are given, respectively.
ipv6 ,
Set the local and/or remote 64-bit interface identifier. Either
one may be omitted. The identifier must be specified in stan-
dard ascii notation of IPv6 addresses (e.g. ::dead:beef). If
the ipv6cp-use-ipaddr option is given, the local identifier is
the local IPv4 address (see above). On systems which supports
a unique persistent id, such as EUI-48 derived from the Ether-
net MAC address, ipv6cp-use-persistent option can be used to
replace the ipv6 , option. Otherwise the identi-
fier is randomized.
active-filter filter-expression
Specifies a packet filter to be applied to data packets to
determine which packets are to be regarded as link activity,
and therefore reset the idle timer, or cause the link to be
brought up in demand-dialling mode. This option is useful in
conjunction with the idle option if there are packets being
sent or received regularly over the link (for example, routing
information packets) which would otherwise prevent the link
from ever appearing to be idle. The filter-expression syntax
is as described for tcpdump(1), except that qualifiers which
are inappropriate for a PPP link, such as ether and arp, are
not permitted. Generally the filter expression should be
enclosed in single-quotes to prevent whitespace in the expres-
sion from being interpreted by the shell. This option is cur-
rently only available under Linux, and requires that the kernel
was configured to include PPP filtering support (CON-
FIG_PPP_FILTER). Note that it is possible to apply different
constraints to incoming and outgoing packets using the inbound
and outbound qualifiers.
allow-ip address(es)
Allow peers to use the given IP address or subnet without
authenticating themselves. The parameter is parsed as for each
element of the list of allowed IP addresses in the secrets
files (see the AUTHENTICATION section below).
allow-number number
Allow peers to connect from the given telephone number. A
trailing '*' character will match all numbers beginning with
the leading part.
bsdcomp nr,nt
Request that the peer compress packets that it sends, using the
BSD-Compress scheme, with a maximum code size of nr bits, and
agree to compress packets sent to the peer with a maximum code
size of nt bits. If nt is not specified, it defaults to the
value given for nr. Values in the range 9 to 15 may be used
for nr and nt; larger values give better compression but con-
sume more kernel memory for compression dictionaries. Alterna-
tively, a value of 0 for nr or nt disables compression in the
corresponding direction. Use nobsdcomp or bsdcomp 0 to disable
BSD-Compress compression entirely.
cdtrcts
Use a non-standard hardware flow control (i.e. DTR/CTS) to con-
trol the flow of data on the serial port. If neither the
crtscts, the nocrtscts, the cdtrcts nor the nocdtrcts option is
given, the hardware flow control setting for the serial port is
left unchanged. Some serial ports (such as Macintosh serial
ports) lack a true RTS output. Such serial ports use this mode
to implement true bi-directional flow control. The sacrifice is
that this flow control mode does not permit using DTR as a
modem control line.
chap-interval n
If this option is given, pppd will rechallenge the peer every n
seconds.
chap-max-challenge n
Set the maximum number of CHAP challenge transmissions to n
(default 10).
chap-restart n
Set the CHAP restart interval (retransmission timeout for chal-
lenges) to n seconds (default 3).
connect-delay n
Wait for up n milliseconds after the connect script finishes
for a valid PPP packet from the peer. At the end of this time,
or when a valid PPP packet is received from the peer, pppd will
commence negotiation by sending its first LCP packet. The
default value is 1000 (1 second). This wait period only
applies if the connect or pty option is used.
debug Enables connection debugging facilities. If this option is
given, pppd will log the contents of all control packets sent
or received in a readable form. The packets are logged through
syslog with facility daemon and level debug. This information
can be directed to a file by setting up /etc/syslog.conf appro-
priately (see syslog.conf(5)).
default-asyncmap
Disable asyncmap negotiation, forcing all control characters to
be escaped for both the transmit and the receive direction.
default-mru
Disable MRU [Maximum Receive Unit] negotiation. With this
option, pppd will use the default MRU value of 1500 bytes for
both the transmit and receive direction.
deflate nr,nt
Request that the peer compress packets that it sends, using the
Deflate scheme, with a maximum window size of 2**nr bytes, and
agree to compress packets sent to the peer with a maximum win-
dow size of 2**nt bytes. If nt is not specified, it defaults
to the value given for nr. Values in the range 9 to 15 may be
used for nr and nt; larger values give better compression but
consume more kernel memory for compression dictionaries.
Alternatively, a value of 0 for nr or nt disables compression
in the corresponding direction. Use nodeflate or deflate 0 to
disable Deflate compression entirely. (Note: pppd requests
Deflate compression in preference to BSD-Compress if the peer
can do either.)
demand Initiate the link only on demand, i.e. when data traffic is
present. With this option, the remote IP address must be spec-
ified by the user on the command line or in an options file.
Pppd will initially configure the interface and enable it for
IP traffic without connecting to the peer. When traffic is
available, pppd will connect to the peer and perform negotia-
tion, authentication, etc. When this is completed, pppd will
commence passing data packets (i.e., IP packets) across the
link.
The demand option implies the persist option. If this
behaviour is not desired, use the nopersist option after the
demand option. The idle and holdoff options are also useful in
conjuction with the demand option.
domain d
Append the domain name d to the local host name for authentica-
tion purposes. For example, if gethostname() returns the name
porsche, but the fully qualified domain name is
porsche.Quotron.COM, you could specify domain Quotron.COM.
Pppd would then use the name porsche.Quotron.COM for looking up
secrets in the secrets file, and as the default name to send to
the peer when authenticating itself to the peer. This option
is privileged.
dryrun With the dryrun option, pppd will print out all the option val-
ues which have been set and then exit, after parsing the com-
mand line and options files and checking the option values, but
before initiating the link. The option values are logged at
level info, and also printed to standard output unless the
device on standard output is the device that pppd would be
using to communicate with the peer.
dump With the dump option, pppd will print out all the option values
which have been set. This option is like the dryrun option
except that pppd proceeds as normal rather than exiting.
endpoint
Sets the endpoint discriminator sent by the local machine to
the peer during multilink negotiation to . The default
is to use the MAC address of the first ethernet interface on
the system, if any, otherwise the IPv4 address corresponding to
the hostname, if any, provided it is not in the multicast or
locally-assigned IP address ranges, or the localhost address.
The endpoint discriminator can be the string null or of the
form type:value, where type is a decimal number or one of the
strings local, IP, MAC, magic, or phone. The value is an IP
address in dotted-decimal notation for the IP type, or a string
of bytes in hexadecimal, separated by periods or colons for the
other types. For the MAC type, the value may also be the name
of an ethernet or similar network interface. This option is
currently only available under Linux.
eap-interval n
If this option is given and pppd authenticates the peer with
EAP (i.e., is the server), pppd will restart EAP authentication
every n seconds. For EAP SRP-SHA1, see also the srp-interval
option, which enables lightweight rechallenge.
eap-max-rreq n
Set the maximum number of EAP Requests to which pppd will
respond (as a client) without hearing EAP Success or Failure.
(Default is 20.)
eap-max-sreq n
Set the maximum number of EAP Requests that pppd will issue (as
a server) while attempting authentication. (Default is 10.)
eap-restart n
Set the retransmit timeout for EAP Requests when acting as a
server (authenticator). (Default is 3 seconds.)
eap-timeout n
Set the maximum time to wait for the peer to send an EAP
Request when acting as a client (authenticatee). (Default is
20 seconds.)
hide-password
When logging the contents of PAP packets, this option causes
pppd to exclude the password string from the log. This is the
default.
holdoff n
Specifies how many seconds to wait before re-initiating the
link after it terminates. This option only has any effect if
the persist or demand option is used. The holdoff period is
not applied if the link was terminated because it was idle.
idle n Specifies that pppd should disconnect if the link is idle for n
seconds. The link is idle when no data packets (i.e. IP pack-
ets) are being sent or received. Note: it is not advisable to
use this option with the persist option without the demand
option. If the active-filter option is given, data packets
which are rejected by the specified activity filter also count
as the link being idle.
ipcp-accept-local
With this option, pppd will accept the peer's idea of our local
IP address, even if the local IP address was specified in an
option.
ipcp-accept-remote
With this option, pppd will accept the peer's idea of its
(remote) IP address, even if the remote IP address was speci-
fied in an option.
ipcp-max-configure n
Set the maximum number of IPCP configure-request transmissions
to n (default 10).
ipcp-max-failure n
Set the maximum number of IPCP configure-NAKs returned before
starting to send configure-Rejects instead to n (default 10).
ipcp-max-terminate n
Set the maximum number of IPCP terminate-request transmissions
to n (default 3).
ipcp-restart n
Set the IPCP restart interval (retransmission timeout) to n
seconds (default 3).
ipparam string
Provides an extra parameter to the ip-up and ip-down scripts.
If this option is given, the string supplied is given as the
6th parameter to those scripts.
ipv6cp-max-configure n
Set the maximum number of IPv6CP configure-request transmis-
sions to n (default 10).
ipv6cp-max-failure n
Set the maximum number of IPv6CP configure-NAKs returned before
starting to send configure-Rejects instead to n (default 10).
ipv6cp-max-terminate n
Set the maximum number of IPv6CP terminate-request transmis-
sions to n (default 3).
ipv6cp-restart n
Set the IPv6CP restart interval (retransmission timeout) to n
seconds (default 3).
ipx Enable the IPXCP and IPX protocols. This option is presently
only supported under Linux, and only if your kernel has been
configured to include IPX support.
ipx-network n
Set the IPX network number in the IPXCP configure request frame
to n, a hexadecimal number (without a leading 0x). There is no
valid default. If this option is not specified, the network
number is obtained from the peer. If the peer does not have
the network number, the IPX protocol will not be started.
ipx-node n:m
Set the IPX node numbers. The two node numbers are separated
from each other with a colon character. The first number n is
the local node number. The second number m is the peer's node
number. Each node number is a hexadecimal number, at most 10
digits long. The node numbers on the ipx-network must be
unique. There is no valid default. If this option is not speci-
fied then the node numbers are obtained from the peer.
ipx-router-name
Set the name of the router. This is a string and is sent to the
peer as information data.
ipx-routing n
Set the routing protocol to be received by this option. More
than one instance of ipx-routing may be specified. The 'none'
option (0) may be specified as the only instance of ipx-rout-
ing. The values may be 0 for NONE, 2 for RIP/SAP, and 4 for
NLSP.
ipxcp-accept-local
Accept the peer's NAK for the node number specified in the ipx-
node option. If a node number was specified, and non-zero, the
default is to insist that the value be used. If you include
this option then you will permit the peer to override the entry
of the node number.
ipxcp-accept-network
Accept the peer's NAK for the network number specified in the
ipx-network option. If a network number was specified, and non-
zero, the default is to insist that the value be used. If you
include this option then you will permit the peer to override
the entry of the node number.
ipxcp-accept-remote
Use the peer's network number specified in the configure
request frame. If a node number was specified for the peer and
this option was not specified, the peer will be forced to use
the value which you have specified.
ipxcp-max-configure n
Set the maximum number of IPXCP configure request frames which
the system will send to n. The default is 10.
ipxcp-max-failure n
Set the maximum number of IPXCP NAK frames which the local sys-
tem will send before it rejects the options. The default value
is 3.
ipxcp-max-terminate n
Set the maximum nuber of IPXCP terminate request frames before
the local system considers that the peer is not listening to
them. The default value is 3.
kdebug n
Enable debugging code in the kernel-level PPP driver. The
argument values depend on the specific kernel driver, but in
general a value of 1 will enable general kernel debug messages.
(Note that these messages are usually only useful for debugging
the kernel driver itself.) For the Linux 2.2.x kernel driver,
the value is a sum of bits: 1 to enable general debug messages,
2 to request that the contents of received packets be printed,
and 4 to request that the contents of transmitted packets be
printed. On most systems, messages printed by the kernel are
logged by syslog(1) to a file as directed in the /etc/sys-
log.conf configuration file.
ktune Enables pppd to alter kernel settings as appropriate. Under
Linux, pppd will enable IP forwarding (i.e. set
/proc/sys/net/ipv4/ip_forward to 1) if the proxyarp option is
used, and will enable the dynamic IP address option (i.e. set
/proc/sys/net/ipv4/ip_dynaddr to 1) in demand mode if the local
address changes.
lcp-echo-failure n
If this option is given, pppd will presume the peer to be dead
if n LCP echo-requests are sent without receiving a valid LCP
echo-reply. If this happens, pppd will terminate the connec-
tion. Use of this option requires a non-zero value for the
lcp-echo-interval parameter. This option can be used to enable
pppd to terminate after the physical connection has been broken
(e.g., the modem has hung up) in situations where no hardware
modem control lines are available.
lcp-echo-interval n
If this option is given, pppd will send an LCP echo-request
frame to the peer every n seconds. Normally the peer should
respond to the echo-request by sending an echo-reply. This
option can be used with the lcp-echo-failure option to detect
that the peer is no longer connected.
lcp-max-configure n
Set the maximum number of LCP configure-request transmissions
to n (default 10).
lcp-max-failure n
Set the maximum number of LCP configure-NAKs returned before
starting to send configure-Rejects instead to n (default 10).
lcp-max-terminate n
Set the maximum number of LCP terminate-request transmissions
to n (default 3).
lcp-restart n
Set the LCP restart interval (retransmission timeout) to n sec-
onds (default 3).
linkname name
Sets the logical name of the link to name. Pppd will create a
file named ppp-name.pid in /var/run (or /etc/ppp on some sys-
tems) containing its process ID. This can be useful in deter-
mining which instance of pppd is responsible for the link to a
given peer system. This is a privileged option.
local Don't use the modem control lines. With this option, pppd will
ignore the state of the CD (Carrier Detect) signal from the
modem and will not change the state of the DTR (Data Terminal
Ready) signal.
logfd n
Send log messages to file descriptor n. Pppd will send log
messages to at most one file or file descriptor (as well as
sending the log messages to syslog), so this option and the
logfile option are mutually exclusive. The default is for pppd
to send log messages to stdout (file descriptor 1), unless the
serial port is already open on stdout.
logfile filename
Append log messages to the file filename (as well as sending
the log messages to syslog). The file is opened with the priv-
ileges of the user who invoked pppd, in append mode.
login Use the system password database for authenticating the peer
using PAP, and record the user in the system wtmp file. Note
that the peer must have an entry in the /etc/ppp/pap-secrets
file as well as the system password database to be allowed
access.
maxconnect n
Terminate the connection when it has been available for network
traffic for n seconds (i.e. n seconds after the first network
control protocol comes up).
maxfail n
Terminate after n consecutive failed connection attempts. A
value of 0 means no limit. The default value is 10.
modem Use the modem control lines. This option is the default. With
this option, pppd will wait for the CD (Carrier Detect) signal
from the modem to be asserted when opening the serial device
(unless a connect script is specified), and it will drop the
DTR (Data Terminal Ready) signal briefly when the connection is
terminated and before executing the connect script. On Ultrix,
this option implies hardware flow control, as for the crtscts
option.
mp Enables the use of PPP multilink; this is an alias for the
'multilink' option. This option is currently only available
under Linux.
mppe-stateful
Allow MPPE to use stateful mode. Stateless mode is still
attempted first. The default is to disallow stateful mode.
mpshortseq
Enables the use of short (12-bit) sequence numbers in multilink
headers, as opposed to 24-bit sequence numbers. This option is
only available under Linux, and only has any effect if multi-
link is enabled (see the multilink option).
mrru n Sets the Maximum Reconstructed Receive Unit to n. The MRRU is
the maximum size for a received packet on a multilink bundle,
and is analogous to the MRU for the individual links. This
option is currently only available under Linux, and only has
any effect if multilink is enabled (see the multilink option).
ms-dns
If pppd is acting as a server for Microsoft Windows clients,
this option allows pppd to supply one or two DNS (Domain Name
Server) addresses to the clients. The first instance of this
option specifies the primary DNS address; the second instance
(if given) specifies the secondary DNS address. (This option
was present in some older versions of pppd under the name dns-
addr.)
ms-wins
If pppd is acting as a server for Microsoft Windows or "Samba"
clients, this option allows pppd to supply one or two WINS
(Windows Internet Name Services) server addresses to the
clients. The first instance of this option specifies the pri-
mary WINS address; the second instance (if given) specifies the
secondary WINS address.
multilink
Enables the use of the PPP multilink protocol. If the peer
also supports multilink, then this link can become part of a
bundle between the local system and the peer. If there is an
existing bundle to the peer, pppd will join this link to that
bundle, otherwise pppd will create a new bundle. See the MUL-
TILINK section below. This option is currently only available
under Linux.
name name
Set the name of the local system for authentication purposes to
name. This is a privileged option. With this option, pppd
will use lines in the secrets files which have name as the sec-
ond field when looking for a secret to use in authenticating
the peer. In addition, unless overridden with the user option,
name will be used as the name to send to the peer when authen-
ticating the local system to the peer. (Note that pppd does
not append the domain name to name.)
noaccomp
Disable Address/Control compression in both directions (send
and receive).
noauth Do not require the peer to authenticate itself. This option is
privileged.
nobsdcomp
Disables BSD-Compress compression; pppd will not request or
agree to compress packets using the BSD-Compress scheme.
noccp Disable CCP (Compression Control Protocol) negotiation. This
option should only be required if the peer is buggy and gets
confused by requests from pppd for CCP negotiation.
nocrtscts
Disable hardware flow control (i.e. RTS/CTS) on the serial
port. If neither the crtscts nor the nocrtscts nor the cdtrcts
nor the nocdtrcts option is given, the hardware flow control
setting for the serial port is left unchanged.
nocdtrcts
This option is a synonym for nocrtscts. Either of these options
will disable both forms of hardware flow control.
nodefaultroute
Disable the defaultroute option. The system administrator who
wishes to prevent users from creating default routes with pppd
can do so by placing this option in the /etc/ppp/options file.
nodeflate
Disables Deflate compression; pppd will not request or agree to
compress packets using the Deflate scheme.
nodetach
Don't detach from the controlling terminal. Without this
option, if a serial device other than the terminal on the stan-
dard input is specified, pppd will fork to become a background
process.
noendpoint
Disables pppd from sending an endpoint discriminator to the
peer or accepting one from the peer (see the MULTILINK section
below). This option should only be required if the peer is
buggy.
noip Disable IPCP negotiation and IP communication. This option
should only be required if the peer is buggy and gets confused
by requests from pppd for IPCP negotiation.
noipv6 Disable IPv6CP negotiation and IPv6 communication. This option
should only be required if the peer is buggy and gets confused
by requests from pppd for IPv6CP negotiation.
noipdefault
Disables the default behaviour when no local IP address is
specified, which is to determine (if possible) the local IP
address from the hostname. With this option, the peer will
have to supply the local IP address during IPCP negotiation
(unless it specified explicitly on the command line or in an
options file).
noipx Disable the IPXCP and IPX protocols. This option should only
be required if the peer is buggy and gets confused by requests
from pppd for IPXCP negotiation.
noktune
Opposite of the ktune option; disables pppd from changing sys-
tem settings.
nolog Do not send log messages to a file or file descriptor. This
option cancels the logfd and logfile options.
nomagic
Disable magic number negotiation. With this option, pppd can-
not detect a looped-back line. This option should only be
needed if the peer is buggy.
nomp Disables the use of PPP multilink. This option is currently
only available under Linux.
nomppe Disables MPPE (Microsoft Point to Point Encryption). This is
the default.
nomppe-40
Disable 40-bit encryption with MPPE.
nomppe-128
Disable 128-bit encryption with MPPE.
nomppe-stateful
Disable MPPE stateful mode. This is the default.
nompshortseq
Disables the use of short (12-bit) sequence numbers in the PPP
multilink protocol, forcing the use of 24-bit sequence numbers.
This option is currently only available under Linux, and only
has any effect if multilink is enabled.
nomultilink
Disables the use of PPP multilink. This option is currently
only available under Linux.
nopcomp
Disable protocol field compression negotiation in both the
receive and the transmit direction.
nopersist
Exit once a connection has been made and terminated. This is
the default unless the persist or demand option has been speci-
fied.
nopredictor1
Do not accept or agree to Predictor-1 compression.
noproxyarp
Disable the proxyarp option. The system administrator who
wishes to prevent users from creating proxy ARP entries with
pppd can do so by placing this option in the /etc/ppp/options
file.
notty Normally, pppd requires a terminal device. With this option,
pppd will allocate itself a pseudo-tty master/slave pair and
use the slave as its terminal device. Pppd will create a child
process to act as a 'character shunt' to transfer characters
between the pseudo-tty master and its standard input and out-
put. Thus pppd will transmit characters on its standard output
and receive characters on its standard input even if they are
not terminal devices. This option increases the latency and
CPU overhead of transferring data over the ppp interface as all
of the characters sent and received must flow through the char-
acter shunt process. An explicit device name may not be given
if this option is used.
novj Disable Van Jacobson style TCP/IP header compression in both
the transmit and the receive direction.
novjccomp
Disable the connection-ID compression option in Van Jacobson
style TCP/IP header compression. With this option, pppd will
not omit the connection-ID byte from Van Jacobson compressed
TCP/IP headers, nor ask the peer to do so.
papcrypt
Indicates that all secrets in the /etc/ppp/pap-secrets file
which are used for checking the identity of the peer are
encrypted, and thus pppd should not accept a password which,
before encryption, is identical to the secret from the
/etc/ppp/pap-secrets file.
pap-max-authreq n
Set the maximum number of PAP authenticate-request transmis-
sions to n (default 10).
pap-restart n
Set the PAP restart interval (retransmission timeout) to n sec-
onds (default 3).
pap-timeout n
Set the maximum time that pppd will wait for the peer to
authenticate itself with PAP to n seconds (0 means no limit).
pass-filter filter-expression
Specifies a packet filter to applied to data packets being sent
or received to determine which packets should be allowed to
pass. Packets which are rejected by the filter are silently
discarded. This option can be used to prevent specific network
daemons (such as routed) using up link bandwidth, or to provide
a very basic firewall capability. The filter-expression syntax
is as described for tcpdump(1), except that qualifiers which
are inappropriate for a PPP link, such as ether and arp, are
not permitted. Generally the filter expression should be
enclosed in single-quotes to prevent whitespace in the expres-
sion from being interpreted by the shell. Note that it is pos-
sible to apply different constraints to incoming and outgoing
packets using the inbound and outbound qualifiers. This option
is currently only available under Linux, and requires that the
kernel was configured to include PPP filtering support (CON-
FIG_PPP_FILTER).
password password-string
Specifies the password to use for authenticating to the peer.
Use of this option is discouraged, as the password is likely to
be visible to other users on the system (for example, by using
ps(1)).
persist
Do not exit after a connection is terminated; instead try to
reopen the connection. The maxfail option still has an effect
on persistent connections.
plugin filename
Load the shared library object file filename as a plugin. This
is a privileged option. If filename does not contain a slash
(/), pppd will look in the /usr/lib/pppd/version directory for
the plugin, where version is the version number of pppd (for
example, 2.4.2).
predictor1
Request that the peer compress frames that it sends using Pre-
dictor-1 compression, and agree to compress transmitted frames
with Predictor-1 if requested. This option has no effect
unless the kernel driver supports Predictor-1 compression.
privgroup group-name
Allows members of group group-name to use privileged options.
This is a privileged option. Use of this option requires care
as there is no guarantee that members of group-name cannot use
pppd to become root themselves. Consider it equivalent to
putting the members of group-name in the kmem or disk group.
proxyarp
Add an entry to this system's ARP [Address Resolution Protocol]
table with the IP address of the peer and the Ethernet address
of this system. This will have the effect of making the peer
appear to other systems to be on the local ethernet.
pty script
Specifies that the command script is to be used to communicate
rather than a specific terminal device. Pppd will allocate
itself a pseudo-tty master/slave pair and use the slave as its
terminal device. The script will be run in a child process
with the pseudo-tty master as its standard input and output.
An explicit device name may not be given if this option is
used. (Note: if the record option is used in conjuction with
the pty option, the child process will have pipes on its stan-
dard input and output.)
receive-all
With this option, pppd will accept all control characters from
the peer, including those marked in the receive asyncmap.
Without this option, pppd will discard those characters as
specified in RFC1662. This option should only be needed if the
peer is buggy.
record filename
Specifies that pppd should record all characters sent and
received to a file named filename. This file is opened in
append mode, using the user's user-ID and permissions. This
option is implemented using a pseudo-tty and a process to
transfer characters between the pseudo-tty and the real serial
device, so it will increase the latency and CPU overhead of
transferring data over the ppp interface. The characters are
stored in a tagged format with timestamps, which can be dis-
played in readable form using the pppdump(8) program.
remotename name
Set the assumed name of the remote system for authentication
purposes to name.
remotenumber number
Set the assumed telephone number of the remote system for
authentication purposes to number.
refuse-chap
With this option, pppd will not agree to authenticate itself to
the peer using CHAP.
refuse-mschap
With this option, pppd will not agree to authenticate itself to
the peer using MS-CHAP.
refuse-mschap-v2
With this option, pppd will not agree to authenticate itself to
the peer using MS-CHAPv2.
refuse-eap
With this option, pppd will not agree to authenticate itself to
the peer using EAP.
refuse-pap
With this option, pppd will not agree to authenticate itself to
the peer using PAP.
require-chap
Require the peer to authenticate itself using CHAP [Challenge
Handshake Authentication Protocol] authentication.
require-mppe
Require the use of MPPE (Microsoft Point to Point Encryption).
This option disables all other compression types. This option
enables both 40-bit and 128-bit encryption. In order for MPPE
to successfully come up, you must have authenticated with
either MS-CHAP or MS-CHAPv2. This option is presently only
supported under Linux, and only if your kernel has been config-
ured to include MPPE support.
require-mppe-40
Require the use of MPPE, with 40-bit encryption.
require-mppe-128
Require the use of MPPE, with 128-bit encryption.
require-mschap
Require the peer to authenticate itself using MS-CHAP [Microsft
Challenge Handshake Authentication Protocol] authentication.
require-mschap-v2
Require the peer to authenticate itself using MS-CHAPv2
[Microsft Challenge Handshake Authentication Protocol, Version
2] authentication.
require-eap
Require the peer to authenticate itself using EAP [Extensible
Authentication Protocol] authentication.
require-pap
Require the peer to authenticate itself using PAP [Password
Authentication Protocol] authentication.
show-password
When logging the contents of PAP packets, this option causes
pppd to show the password string in the log message.
silent With this option, pppd will not transmit LCP packets to initi-
ate a connection until a valid LCP packet is received from the
peer (as for the 'passive' option with ancient versions of
pppd).
srp-interval n
If this parameter is given and pppd uses EAP SRP-SHA1 to
authenticate the peer (i.e., is the server), then pppd will use
the optional lightweight SRP rechallenge mechanism at intervals
of n seconds. This option is faster than eap-interval reau-
thentication because it uses a hash-based mechanism and does
not derive a new session key.
srp-pn-secret string
Set the long-term pseudonym-generating secret for the server.
This value is optional and if set, needs to be known at the
server (authenticator) side only, and should be different for
each server (or poll of identical servers). It is used along
with the current date to generate a key to encrypt and decrypt
the client's identity contained in the pseudonym.
srp-use-pseudonym
When operating as an EAP SRP-SHA1 client, attempt to use the
pseudonym stored in ~/.ppp_psuedonym first as the identity, and
save in this file any pseudonym offered by the peer during
authentication.
sync Use synchronous HDLC serial encoding instead of asynchronous.
The device used by pppd with this option must have sync sup-
port. Currently supports Microgate SyncLink adapters under
Linux and FreeBSD 2.2.8 and later.
unit num
Sets the ppp unit number (for a ppp0 or ppp1 etc interface
name) for outbound connections.
updetach
With this option, pppd will detach from its controlling termi-
nal once it has successfully established the ppp connection (to
the point where the first network control protocol, usually the
IP control protocol, has come up).
usehostname
Enforce the use of the hostname (with domain name appended, if
given) as the name of the local system for authentication pur-
poses (overrides the name option). This option is not normally
needed since the name option is privileged.
usepeerdns
Ask the peer for up to 2 DNS server addresses. The addresses
supplied by the peer (if any) are passed to the /etc/ppp/ip-up
script in the environment variables DNS1 and DNS2, and the
environment variable USEPEERDNS will be set to 1. In addition,
pppd will create an /etc/ppp/resolv.conf file containing one or
two nameserver lines with the address(es) supplied by the peer.
user name
Sets the name used for authenticating the local system to the
peer to name.
vj-max-slots n
Sets the number of connection slots to be used by the Van
Jacobson TCP/IP header compression and decompression code to n,
which must be between 2 and 16 (inclusive).
welcome script
Run the executable or shell command specified by script before
initiating PPP negotiation, after the connect script (if any)
has completed. A value for this option from a privileged
source cannot be overridden by a non-privileged user.
xonxoff
Use software flow control (i.e. XON/XOFF) to control the flow
of data on the serial port.
OPTIONS FILES
Options can be taken from files as well as the command line. Pppd
reads options from the files /etc/ppp/options, ~/.ppprc and
/etc/ppp/options.ttyname (in that order) before processing the options
on the command line. (In fact, the command-line options are scanned
to find the terminal name before the options.ttyname file is read.)
In forming the name of the options.ttyname file, the initial /dev/ is
removed from the terminal name, and any remaining / characters are
replaced with dots.
An options file is parsed into a series of words, delimited by whites-
pace. Whitespace can be included in a word by enclosing the word in
double-quotes ("). A backslash (\) quotes the following character. A
hash (#) starts a comment, which continues until the end of the line.
There is no restriction on using the file or call options within an
options file.
SECURITY
pppd provides system administrators with sufficient access control
that PPP access to a server machine can be provided to legitimate
users without fear of compromising the security of the server or the
network it's on. This control is provided through restrictions on
which IP addresses the peer may use, based on its authenticated iden-
tity (if any), and through restrictions on which options a non-privi-
leged user may use. Several of pppd's options are privileged, in par-
ticular those which permit potentially insecure configurations; these
options are only accepted in files which are under the control of the
system administrator, or if pppd is being run by root.
The default behaviour of pppd is to allow an unauthenticated peer to
use a given IP address only if the system does not already have a
route to that IP address. For example, a system with a permanent con-
nection to the wider internet will normally have a default route, and
thus all peers will have to authenticate themselves in order to set up
a connection. On such a system, the auth option is the default. On
the other hand, a system where the PPP link is the only connection to
the internet will not normally have a default route, so the peer will
be able to use almost any IP address without authenticating itself.
As indicated above, some security-sensitive options are privileged,
which means that they may not be used by an ordinary non-privileged
user running a setuid-root pppd, either on the command line, in the
user's ~/.ppprc file, or in an options file read using the file
option. Privileged options may be used in /etc/ppp/options file or in
an options file read using the call option. If pppd is being run by
the root user, privileged options can be used without restriction.
When opening the device, pppd uses either the invoking user's user ID
or the root UID (that is, 0), depending on whether the device name was
specified by the user or the system administrator. If the device name
comes from a privileged source, that is, /etc/ppp/options or an
options file read using the call option, pppd uses full root privi-
leges when opening the device. Thus, by creating an appropriate file
under /etc/ppp/peers, the system administrator can allow users to
establish a ppp connection via a device which they would not normally
have permission to access. Otherwise pppd uses the invoking user's
real UID when opening the device.
AUTHENTICATION
Authentication is the process whereby one peer convinces the other of
its identity. This involves the first peer sending its name to the
other, together with some kind of secret information which could only
come from the genuine authorized user of that name. In such an
exchange, we will call the first peer the "client" and the other the
"server". The client has a name by which it identifies itself to the
server, and the server also has a name by which it identifies itself
to the client. Generally the genuine client shares some secret (or
password) with the server, and authenticates itself by proving that it
knows that secret. Very often, the names used for authentication cor-
respond to the internet hostnames of the peers, but this is not essen-
tial.
At present, pppd supports three authentication protocols: the Password
Authentication Protocol (PAP), Challenge Handshake Authentication Pro-
tocol (CHAP), and Extensible Authentication Protocol (EAP). PAP
involves the client sending its name and a cleartext password to the
server to authenticate itself. In contrast, the server initiates the
CHAP authentication exchange by sending a challenge to the client (the
challenge packet includes the server's name). The client must respond
with a response which includes its name plus a hash value derived from
the shared secret and the challenge, in order to prove that it knows
the secret. EAP supports CHAP-style authentication, and also includes
the SRP-SHA1 mechanism, which is resistant to dictionary-based attacks
and does not require a cleartext password on the server side.
The PPP protocol, being symmetrical, allows both peers to require the
other to authenticate itself. In that case, two separate and indepen-
dent authentication exchanges will occur. The two exchanges could use
different authentication protocols, and in principle, different names
could be used in the two exchanges.
The default behaviour of pppd is to agree to authenticate if
requested, and to not require authentication from the peer. However,
pppd will not agree to authenticate itself with a particular protocol
if it has no secrets which could be used to do so.
Pppd stores secrets for use in authentication in secrets files
(/etc/ppp/pap-secrets for PAP, /etc/ppp/chap-secrets for CHAP, MS-
CHAP, MS-CHAPv2, and EAP MD5-Challenge, and /etc/ppp/srp-secrets for
EAP SRP-SHA1). All secrets files have the same format. The secrets
files can contain secrets for pppd to use in authenticating itself to
other systems, as well as secrets for pppd to use when authenticating
other systems to itself.
Each line in a secrets file contains one secret. A given secret is
specific to a particular combination of client and server - it can
only be used by that client to authenticate itself to that server.
Thus each line in a secrets file has at least 3 fields: the name of
the client, the name of the server, and the secret. These fields may
be followed by a list of the IP addresses that the specified client
may use when connecting to the specified server.
A secrets file is parsed into words as for a options file, so the
client name, server name and secrets fields must each be one word,
with any embedded spaces or other special characters quoted or
escaped. Note that case is significant in the client and server names
and in the secret.
If the secret starts with an '@', what follows is assumed to be the
name of a file from which to read the secret. A "*" as the client or
server name matches any name. When selecting a secret, pppd takes the
best match, i.e. the match with the fewest wildcards.
Any following words on the same line are taken to be a list of accept-
able IP addresses for that client. If there are only 3 words on the
line, or if the first word is "-", then all IP addresses are disal-
lowed. To allow any address, use "*". A word starting with "!"
indicates that the specified address is not acceptable. An address
may be followed by "/" and a number n, to indicate a whole subnet,
i.e. all addresses which have the same value in the most significant n
bits. In this form, the address may be followed by a plus sign ("+")
to indicate that one address from the subnet is authorized, based on
the ppp network interface unit number in use. In this case, the host
part of the address will be set to the unit number plus one.
Thus a secrets file contains both secrets for use in authenticating
other hosts, plus secrets which we use for authenticating ourselves to
others. When pppd is authenticating the peer (checking the peer's
identity), it chooses a secret with the peer's name in the first field
and the name of the local system in the second field. The name of the
local system defaults to the hostname, with the domain name appended
if the domain option is used. This default can be overridden with the
name option, except when the usehostname option is used. (For EAP
SRP-SHA1, see the srp-entry(8) utility for generating proper validator
entries to be used in the "secret" field.)
When pppd is choosing a secret to use in authenticating itself to the
peer, it first determines what name it is going to use to identify
itself to the peer. This name can be specified by the user with the
user option. If this option is not used, the name defaults to the
name of the local system, determined as described in the previous
paragraph. Then pppd looks for a secret with this name in the first
field and the peer's name in the second field. Pppd will know the
name of the peer if CHAP or EAP authentication is being used, because
the peer will have sent it in the challenge packet. However, if PAP
is being used, pppd will have to determine the peer's name from the
options specified by the user. The user can specify the peer's name
directly with the remotename option. Otherwise, if the remote IP
address was specified by a name (rather than in numeric form), that
name will be used as the peer's name. Failing that, pppd will use the
null string as the peer's name.
When authenticating the peer with PAP, the supplied password is first
compared with the secret from the secrets file. If the password
doesn't match the secret, the password is encrypted using crypt() and
checked against the secret again. Thus secrets for authenticating the
peer can be stored in encrypted form if desired. If the papcrypt
option is given, the first (unencrypted) comparison is omitted, for
better security.
Furthermore, if the login option was specified, the username and pass-
word are also checked against the system password database. Thus, the
system administrator can set up the pap-secrets file to allow PPP
access only to certain users, and to restrict the set of IP addresses
that each user can use. Typically, when using the login option, the
secret in /etc/ppp/pap-secrets would be "", which will match any pass-
word supplied by the peer. This avoids the need to have the same
secret in two places.
Authentication must be satisfactorily completed before IPCP (or any
other Network Control Protocol) can be started. If the peer is
required to authenticate itself, and fails to do so, pppd will termi-
nated the link (by closing LCP). If IPCP negotiates an unacceptable
IP address for the remote host, IPCP will be closed. IP packets can
only be sent or received when IPCP is open.
In some cases it is desirable to allow some hosts which can't authen-
ticate themselves to connect and use one of a restricted set of IP
addresses, even when the local host generally requires authentication.
If the peer refuses to authenticate itself when requested, pppd takes
that as equivalent to authenticating with PAP using the empty string
for the username and password. Thus, by adding a line to the pap-
secrets file which specifies the empty string for the client and pass-
word, it is possible to allow restricted access to hosts which refuse
to authenticate themselves.
ROUTING
When IPCP negotiation is completed successfully, pppd will inform the
kernel of the local and remote IP addresses for the ppp interface.
This is sufficient to create a host route to the remote end of the
link, which will enable the peers to exchange IP packets. Communica-
tion with other machines generally requires further modification to
routing tables and/or ARP (Address Resolution Protocol) tables. In
most cases the defaultroute and/or proxyarp options are sufficient for
this, but in some cases further intervention is required. The
/etc/ppp/ip-up script can be used for this.
Sometimes it is desirable to add a default route through the remote
host, as in the case of a machine whose only connection to the Inter-
net is through the ppp interface. The defaultroute option causes pppd
to create such a default route when IPCP comes up, and delete it when
the link is terminated.
In some cases it is desirable to use proxy ARP, for example on a
server machine connected to a LAN, in order to allow other hosts to
communicate with the remote host. The proxyarp option causes pppd to
look for a network interface on the same subnet as the remote host (an
interface supporting broadcast and ARP, which is up and not a point-
to-point or loopback interface). If found, pppd creates a permanent,
published ARP entry with the IP address of the remote host and the
hardware address of the network interface found.
When the demand option is used, the interface IP addresses have
already been set at the point when IPCP comes up. If pppd has not
been able to negotiate the same addresses that it used to configure
the interface (for example when the peer is an ISP that uses dynamic
IP address assignment), pppd has to change the interface IP addresses
to the negotiated addresses. This may disrupt existing connections,
and the use of demand dialling with peers that do dynamic IP address
assignment is not recommended.
MULTILINK
Multilink PPP provides the capability to combine two or more PPP links
between a pair of machines into a single 'bundle', which appears as a
single virtual PPP link which has the combined bandwidth of the indi-
vidual links. Currently, multilink PPP is only supported under Linux.
Pppd detects that the link it is controlling is connected to the same
peer as another link using the peer's endpoint discriminator and the
authenticated identity of the peer (if it authenticates itself). The
endpoint discriminator is a block of data which is hopefully unique
for each peer. Several types of data can be used, including locally-
assigned strings of bytes, IP addresses, MAC addresses, randomly
strings of bytes, or E-164 phone numbers. The endpoint discriminator
sent to the peer by pppd can be set using the endpoint option.
In circumstances the peer may send no endpoint discriminator or a non-
unique value. The optional bundle option adds an extra string which
is added to the peer's endpoint discriminator and authenticated iden-
tity when matching up links to be joined together in a bundle. The
bundle option can also be used to allow the establishment of multiple
bundles between the local system and the peer. Pppd uses a TDB
database in /var/run/pppd.tdb to match up links.
Assuming that multilink is enabled and the peer is willing to
negotiate multilink, then when pppd is invoked to bring up the first
link to the peer, it will detect that no other link is connected to
the peer and create a new bundle, that is, another ppp network inter-
face unit. When another pppd is invoked to bring up another link to
the peer, it will detect the existing bundle and join its link to it.
Currently, if the first pppd terminates (for example, because of a
hangup or a received signal) the bundle is destroyed.
EXAMPLES
The following examples assume that the /etc/ppp/options file contains
the auth option (as in the default /etc/ppp/options file in the ppp
distribution).
Probably the most common use of pppd is to dial out to an ISP. This
can be done with a command such as
pppd call isp
where the /etc/ppp/peers/isp file is set up by the system administra-
tor to contain something like this:
ttyS0 19200 crtscts
connect '/usr/sbin/chat -v -f /etc/ppp/chat-isp'
noauth
In this example, we are using chat to dial the ISP's modem and go
through any logon sequence required. The /etc/ppp/chat-isp file con-
tains the script used by chat; it could for example contain something
like this:
ABORT "NO CARRIER"
ABORT "NO DIALTONE"
ABORT "ERROR"
ABORT "NO ANSWER"
ABORT "BUSY"
ABORT "Username/Password Incorrect"
"" "at"
OK "at&d0&c1"
OK "atdt2468135"
"name:" "^Umyuserid"
"word:" "\qmypassword"
"ispts" "\q^Uppp"
"~-^Uppp-~"
See the chat(8) man page for details of chat scripts.
Pppd can also be used to provide a dial-in ppp service for users. If
the users already have login accounts, the simplest way to set up the
ppp service is to let the users log in to their accounts and run pppd
(installed setuid-root) with a command such as
pppd proxyarp
To allow a user to use the PPP facilities, you need to allocate an IP
address for that user's machine and create an entry in /etc/ppp/pap-
secrets, /etc/ppp/chap-secrets, or /etc/ppp/srp-secrets (depending on
which authentication method the PPP implementation on the user's
machine supports), so that the user's machine can authenticate itself.
For example, if Joe has a machine called "joespc" that is to be
allowed to dial in to the machine called "server" and use the IP
address joespc.my.net, you would add an entry like this to
/etc/ppp/pap-secrets or /etc/ppp/chap-secrets:
joespc server "joe's secret" joespc.my.net
(See srp-entry(8) for a means to generate the server's entry when SRP-
SHA1 is in use.) Alternatively, you can create a username called (for
example) "ppp", whose login shell is pppd and whose home directory is
/etc/ppp. Options to be used when pppd is run this way can be put in
/etc/ppp/.ppprc.
If your serial connection is any more complicated than a piece of
wire, you may need to arrange for some control characters to be
escaped. In particular, it is often useful to escape XON (^Q) and
XOFF (^S), using asyncmap a0000. If the path includes a telnet, you
probably should escape ^] as well (asyncmap 200a0000). If the path
includes an rlogin, you will need to use the escape ff option on the
end which is running the rlogin client, since many rlogin implementa-
tions are not transparent; they will remove the sequence [0xff, 0xff,
0x73, 0x73, followed by any 8 bytes] from the stream.
DIAGNOSTICS
Messages are sent to the syslog daemon using facility LOG_DAEMON.
(This can be overridden by recompiling pppd with the macro LOG_PPP
defined as the desired facility.) See the syslog(8) documentation for
details of where the syslog daemon will write the messages. On most
systems, the syslog daemon uses the /etc/syslog.conf file to specify
the destination(s) for syslog messages. You may need to edit that
file to suit.
The debug option causes the contents of all control packets sent or
received to be logged, that is, all LCP, PAP, CHAP, EAP, or IPCP pack-
ets. This can be useful if the PPP negotiation does not succeed or if
authentication fails. If debugging is enabled at compile time, the
debug option also causes other debugging messages to be logged.
Debugging can also be enabled or disabled by sending a SIGUSR1 signal
to the pppd process. This signal acts as a toggle.
EXIT STATUS
The exit status of pppd is set to indicate whether any error was
detected, or the reason for the link being terminated. The values
used are:
0 Pppd has detached, or otherwise the connection was successfully
established and terminated at the peer's request.
1 An immediately fatal error of some kind occurred, such as an
essential system call failing, or running out of virtual mem-
ory.
2 An error was detected in processing the options given, such as
two mutually exclusive options being used.
3 Pppd is not setuid-root and the invoking user is not root.
4 The kernel does not support PPP, for example, the PPP kernel
driver is not included or cannot be loaded.
5 Pppd terminated because it was sent a SIGINT, SIGTERM or SIGHUP
signal.
6 The serial port could not be locked.
7 The serial port could not be opened.
8 The connect script failed (returned a non-zero exit status).
9 The command specified as the argument to the pty option could
not be run.
10 The PPP negotiation failed, that is, it didn't reach the point
where at least one network protocol (e.g. IP) was running.
11 The peer system failed (or refused) to authenticate itself.
12 The link was established successfully and terminated because it
was idle.
13 The link was established successfully and terminated because
the connect time limit was reached.
14 Callback was negotiated and an incoming call should arrive
shortly.
15 The link was terminated because the peer is not responding to
echo requests.
16 The link was terminated by the modem hanging up.
17 The PPP negotiation failed because serial loopback was
detected.
18 The init script failed (returned a non-zero exit status).
19 We failed to authenticate ourselves to the peer.
SCRIPTS
Pppd invokes scripts at various stages in its processing which can be
used to perform site-specific ancillary processing. These scripts are
usually shell scripts, but could be executable code files instead.
Pppd does not wait for the scripts to finish. The scripts are exe-
cuted as root (with the real and effective user-id set to 0), so that
they can do things such as update routing tables or run privileged
daemons. Be careful that the contents of these scripts do not compro-
mise your system's security. Pppd runs the scripts with standard
input, output and error redirected to /dev/null, and with an environ-
ment that is empty except for some environment variables that give
information about the link. The environment variables that pppd sets
are:
DEVICE The name of the serial tty device being used.
IFNAME The name of the network interface being used.
IPLOCAL
The IP address for the local end of the link. This is only set
when IPCP has come up.
IPREMOTE
The IP address for the remote end of the link. This is only
set when IPCP has come up.
PEERNAME
The authenticated name of the peer. This is only set if the
peer authenticates itself.
SPEED The baud rate of the tty device.
ORIG_UID
The real user-id of the user who invoked pppd.
PPPLOGNAME
The username of the real user-id that invoked pppd. This is
always set.
For the ip-down and auth-down scripts, pppd also sets the following
variables giving statistics for the connection:
CONNECT_TIME
The number of seconds from when the PPP negotiation started
until the connection was terminated.
BYTES_SENT
The number of bytes sent (at the level of the serial port) dur-
ing the connection.
BYTES_RCVD
The number of bytes received (at the level of the serial port)
during the connection.
LINKNAME
The logical name of the link, set with the linkname option.
DNS1 If the peer supplies DNS server addresses, this variable is set
to the first DNS server address supplied.
DNS2 If the peer supplies DNS server addresses, this variable is set
to the second DNS server address supplied.
Pppd invokes the following scripts, if they exist. It is not an error
if they don't exist.
/etc/ppp/auth-up
A program or script which is executed after the remote system
successfully authenticates itself. It is executed with the
parameters
interface-name peer-name user-name tty-device speed
Note that this script is not executed if the peer doesn't
authenticate itself, for example when the noauth option is
used.
/etc/ppp/auth-down
A program or script which is executed when the link goes down,
if /etc/ppp/auth-up was previously executed. It is executed in
the same manner with the same parameters as /etc/ppp/auth-up.
/etc/ppp/ip-up
A program or script which is executed when the link is avail-
able for sending and receiving IP packets (that is, IPCP has
come up). It is executed with the parameters
interface-name tty-device speed local-IP-address remote-IP-
address ipparam
/etc/ppp/ip-down
A program or script which is executed when the link is no
longer available for sending and receiving IP packets. This
script can be used for undoing the effects of the /etc/ppp/ip-
up script. It is invoked in the same manner and with the same
parameters as the ip-up script.
/etc/ppp/ipv6-up
Like /etc/ppp/ip-up, except that it is executed when the link
is available for sending and receiving IPv6 packets. It is exe-
cuted with the parameters
interface-name tty-device speed local-link-local-address
remote-link-local-address ipparam
/etc/ppp/ipv6-down
Similar to /etc/ppp/ip-down, but it is executed when IPv6 pack-
ets can no longer be transmitted on the link. It is executed
with the same parameters as the ipv6-up script.
/etc/ppp/ipx-up
A program or script which is executed when the link is avail-
able for sending and receiving IPX packets (that is, IPXCP has
come up). It is executed with the parameters
interface-name tty-device speed network-number local-IPX-node-
address remote-IPX-node-address local-IPX-routing-protocol
remote-IPX-routing-protocol local-IPX-router-name remote-IPX-
router-name ipparam pppd-pid
The local-IPX-routing-protocol and remote-IPX-routing-protocol
field may be one of the following:
NONE to indicate that there is no routing protocol
RIP to indicate that RIP/SAP should be used
NLSP to indicate that Novell NLSP should be used
RIP NLSP to indicate that both RIP/SAP and NLSP should be used
/etc/ppp/ipx-down
A program or script which is executed when the link is no
longer available for sending and receiving IPX packets. This
script can be used for undoing the effects of the /etc/ppp/ipx-
up script. It is invoked in the same manner and with the same
parameters as the ipx-up script.
FILES
/var/run/pppn.pid (BSD or Linux), /etc/ppp/pppn.pid (others)
Process-ID for pppd process on ppp interface unit n.
/var/run/ppp-name.pid (BSD or Linux),
/etc/ppp/ppp-name.pid (others) Process-ID for pppd process for
logical link name (see the linkname option).
/etc/ppp/pap-secrets
Usernames, passwords and IP addresses for PAP authentication.
This file should be owned by root and not readable or writable
by any other user. Pppd will log a warning if this is not the
case.
/etc/ppp/chap-secrets
Names, secrets and IP addresses for CHAP/MS-CHAP/MS-CHAPv2
authentication. As for /etc/ppp/pap-secrets, this file should
be owned by root and not readable or writable by any other
user. Pppd will log a warning if this is not the case.
/etc/ppp/srp-secrets
Names, secrets, and IP addresses for EAP authentication. As
for /etc/ppp/pap-secrets, this file should be owned by root and
not readable or writable by any other user. Pppd will log a
warning if this is not the case.
~/.ppp_pseudonym
Saved client-side SRP-SHA1 pseudonym. See the srp-use-
pseudonym option for details.
/etc/ppp/options
System default options for pppd, read before user default
options or command-line options.
~/.ppprc
User default options, read before /etc/ppp/options.ttyname.
/etc/ppp/options.ttyname
System default options for the serial port being used, read
after ~/.ppprc. In forming the ttyname part of this filename,
an initial /dev/ is stripped from the port name (if present),
and any slashes in the remaining part are converted to dots.
/etc/ppp/peers
A directory containing options files which may contain privi-
leged options, even if pppd was invoked by a user other than
root. The system administrator can create options files in
this directory to permit non-privileged users to dial out with-
out requiring the peer to authenticate, but only to certain
trusted peers.
SEE ALSO
RFC1144
Jacobson, V. Compressing TCP/IP headers for low-speed serial
links. February 1990.
RFC1321
Rivest, R. The MD5 Message-Digest Algorithm. April 1992.
RFC1332
McGregor, G. PPP Internet Protocol Control Protocol (IPCP).
May 1992.
RFC1334
Lloyd, B.; Simpson, W.A. PPP authentication protocols. Octo-
ber 1992.
RFC1661
Simpson, W.A. The Point-to-Point Protocol (PPP). July 1994.
RFC1662
Simpson, W.A. PPP in HDLC-like Framing. July 1994.
RFC2284
Blunk, L.; Vollbrecht, J., PPP Extensible Authentication Proto-
col (EAP). March 1998.
RFC2472
Haskin, D. IP Version 6 over PPP December 1998.
RFC2945
Wu, T., The SRP Authentication and Key Exchange System Septem-
ber 2000.
draft-ietf-pppext-eap-srp-03.txt
Carlson, J.; et al., EAP SRP-SHA1 Authentication Protocol.
July 2001.
NOTES
Some limited degree of control can be exercised over a running pppd
process by sending it a signal from the list below.
SIGINT, SIGTERM
These signals cause pppd to terminate the link (by closing
LCP), restore the serial device settings, and exit.
SIGHUP This signal causes pppd to terminate the link, restore the
serial device settings, and close the serial device. If the
persist or demand option has been specified, pppd will try to
reopen the serial device and start another connection (after
the holdoff period). Otherwise pppd will exit. If this signal
is received during the holdoff period, it causes pppd to end
the holdoff period immediately.
SIGUSR1
This signal toggles the state of the debug option.
SIGUSR2
This signal causes pppd to renegotiate compression. This can
be useful to re-enable compression after it has been disabled
as a result of a fatal decompression error. (Fatal decompres-
sion errors generally indicate a bug in one or other implemen-
tation.)
AUTHORS
Paul Mackerras (Paul.Mackerras@samba.org), based on earlier work by
Drew Perkins, Brad Clements, Karl Fox, Greg Christy, and Brad Parker.
PPPD(8)
UNIX/Linux commands referenced on this page: