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Linux in a Nutshell

This directory of Linux commands is from Linux in a Nutshell, 5th Edition.

Click on any of the 687 commands below to get a description and list of available options. All links in the command summaries point to the online version of the book on Safari Bookshelf.

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pppd [tty] [speed] [options]

System administration command. PPP stands for the Point-to-Point Protocol; it allows datagram transmission over a serial connection. pppd attempts to configure tty for PPP (searching in /dev) or, by default, the controlling terminal. You can also specify a baud rate of speed. pppd accepts many options. Only the most common options are listed here.


[local_IP_address] :[remote_IP_address]

Specify the local and/or remote interface IP addresses, as hostnames or numeric addresses.

asyncmap map

Specify which control characters cannot pass over the line. map should be a 32-bit hex number, where each bit represents a character to escape. For example, bit 00000001 represents the character 0x00; bit 80000000 represents the character 0x1f or _. You may specify multiple characters.


Require self-authentication by peers before allowing packets to move.

call file

Read options from file in /etc/ppp/peers/. Unlike the file option, call file may contain privileged options, even when pppd is not run by root.

connect command

Connect as specified by command, which may be a binary or shell command.


Use hardware flow control.


Log contents of control packets to syslogd.


Add a new default route in which the peer is the gateway. When the connection shuts down, remove the route.


Operate in the foreground. By default, pppd forks and operates in the background.

disconnect command

Close the connection as specified by command, which may be a binary or shell command.

escape character-list

Escape all characters in character-list, which should be a comma-separated list of hex numbers. You cannot escape 0x20-0x3f or 0x5e.

file file

Consult file for options.

init script

Run specified command or shell script to initialize the serial line.


Allow only pppd to access the device.

mru bytes

Refuse packets of more than bytes bytes.

mtu bytes

Do not send packets of more than bytes bytes.

passive, -p

Do not exit if peer does not respond to attempts to initiate a connection. Instead, wait for a valid packet from the peer.


Send no packets until after receiving one.



pppd's process ID. The n in is the number of the PPP interface unit corresponding to this pppd process.


Binary or script to be executed when the PPP link becomes active.


Binary or script to be executed when the PPP link goes down.


Contains usernames, passwords, and IP addresses for use in PAP authentication.


System defaults. Options in this file are set before the command-line options.


The user's default options. These are read before command-line options but after the system defaults.


Name of the default serial port.

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