This manual documents version 1.9.1 of the gnu networking utilities.
Copyright © 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.
The GNU Network Utilities is a distribution of common networking utilities and servers, including for example ping, traceroute and ftp.
This manual is a work in progress: many sections make no attempt to explain basic concepts in a way suitable for novices. Thus, if you are interested, please get involved in improving this manual. The entire gnu community will benefit.
Please report bugs to email@example.com. Remember to include the version number, machine architecture, input files, and any other information needed to reproduce the bug: your input, what you expected, what you got, and why it is wrong. Diffs are welcome, but please include a description of the problem as well, since this is sometimes difficult to infer.
The individual utilities were originally derived from the 4.4BSDLite2 distribution, although some of them have more or less been rewritten. What you are reading now is the authoritative and complete documentation for these utilities; the man pages are now automatically generated.
Many features were integrated from NetBSD, OpenBSD, FreeBSD and GNU/Linux, the merges were done by a group of dedicated hackers (in no particular order): Jeff Bailey, Marcus Brinkmann, Michael Vogt, Bernhard Rosenkraenzer, Kaveh R. Ghazi, NIIBE Yutaka, Nathan Neulinger, Jeff Smith, Dan Stromberg, David O'Shea, Frederic Goudal, Gerald Combs, Joachim Gabler, Marco D'Itri, Sergey Poznyakoff, and many more.
Certain options are available in all these programs. Rather than writing identical descriptions for each of the programs, they are described here. (In fact, every gnu program accepts, or should accept, these options.)
Many of these programs take arbitrary strings as arguments. In those cases, --help and --version are taken as these options only if there is one and exactly one command line argument.
Nearly every command invocation yields an integral exit status that can be used to change how other commands work. For the vast majority of commands, an exit status of zero indicates success. Failure is indicated by a nonzero value — typically ‘1’, though it may differ on unusual platforms, as POSIX requires only that it be nonzero.
hostname is a program to show or set the name of host system.
hostname [option...] [name]
logger is a program to send entries to system log. It provides a shell command interface similar to the system log module. See Syslog, for details.
logger [option...] [message]
Both options are most influencial when the target host is named using
a symbolic name, but numerical addresses for host or source must also
match if either of --ipv4 or --ipv6 is stated.
where host is the remote host name or IP address, and the
optional port is a decimal port number or symbolic service
name from /etc/services. If port is not specified,
the port number corresponding to the ‘syslog’ service is used.
If a numerical IPv6 address is given without a port specification,
then the address must be enclosed within brackets (like [::1]).
The actual list of supported facilities and levels is system specific.
The options are followed by the message which should be written to the log. If not specified, and the -f flag is not provided, standard input is logged.
The logger utility exits 0 on success, and >0 if an error occurs.
The following examples illustrate the usage of the logger command:
logger System rebooted
command 2>&1 | logger -p local0.notice -t cmd
logger -p daemon.warn -h logger.runasimi.org -S 10.10.10.1 --file warnings
ping uses the ICMP protocol's mandatory
datagram to elicit an ICMP
ECHO_RESPONSE from a host or
ECHO_REQUEST datagrams (pings) have an IP and
ICMP header, followed by a struct timeval and then an arbitrary
number of pad bytes used to fill out the packet. Synopsis:
ping [option...] host...
RECORD_ROUTEfield in the ECHO_REQUEST packet and displays the route buffer on returned packets. Note that the IP header is only large enough for nine such routes. Many hosts ignore or discard this option.
When using ping for fault isolation, it should first be run on the local host, to verify that the local network interface is up and running. Then, hosts and gateways further and further away should be pinged. Round-trip times and packet loss statistics are computed. If duplicate packets are received, they are not included in the packet loss calculation, although the round trip time of these packets is used in calculating the minimum/average/maximum round-trip time numbers. When the specified number of packets have been sent (and received) or if the program is terminated with a ‘SIGINT’, a brief summary is displayed.
This program is intended for use in network testing, measurement and management. Because of the load it can impose on the network, it is unwise to use ping during normal operations or from automated scripts.
Ping will report duplicate and damaged packets. Duplicate packets should never occur, and seem to be caused by inappropriate link-level retransmissions. Duplicates may occur in many situations and are rarely (if ever) a good sign, although the presence of low levels of duplicates may not always be cause for alarm.
Damaged packets are obviously serious cause for alarm and often indicate broken hardware somewhere in the ping packet's path (in the network or in the hosts).
The (inter)network layer should never treat packets differently depending on the data contained in the data portion. Unfortunately, data-dependent problems have been known to sneak into networks and remain undetected for long periods of time. In many cases the particular pattern that will have problems is something that doesn't have sufficient “transitions”, such as all ones or all zeros, or a pattern right at the edge, such as almost all zeros. It isn't necessarily enough to specify a data pattern of all zeros (for example) on the command line because the pattern that is of interest is at the data link level, and the relationship between what you type and what the controllers transmit can be complicated.
This means that if you have a data-dependent problem you will probably have to do a lot of testing to find it. If you are lucky, you may manage to find a file that either can't be sent across your network or that takes much longer to transfer than other similar length files. You can then examine this file for repeated patterns that you can test using the -p option of ping.
The TTL, Time To Live value of an IP packet represents the maximum number of IP routers that the packet can go through before being thrown away. In current practice you can expect each router in the Internet to decrement the TTL field by exactly one.
The TCP/IP specification states that the TTL field for TCP packets should be set to 60, but many systems use smaller values (4.3 BSD uses 30, 4.2 used 15).
The maximum possible value of this field is 255, and most UNIX systems
set the TTL field of ICMP (
ECHO_REQUEST) packets to 255. This
is why you will find you can ping some hosts, but not reach them with
telnet or ftp.
In normal operation ping prints the TTL value from the packet it receives. When a remote system receives a ICMP packet, it can do one of three things with the TTL field in its response:
TTLvalue in the received packet will be 255 minus the number of routers in the path from the remote system to the pinging host.
Many hosts and gateways ignore the
RECORD_ROUTE field, since
the maximum IP header length is far to small to hold all the routes.
There's not much that can be done about this.
Flood pinging is not recommended in general, and flood pinging the broadcast address should only be done under very controlled conditions.
traceroute traces the route packets take to a host. Synopsis:
traceroute [option...] host
whois [OPTION]... OBJECT...
ftp is the user interface for FTP, File Transfer Protocol. The program allows a user to transfer files to and from a remote network site. Synopsis:
ftp [option...] [host [port]]
The client host with which ftp is to communicate may be specified on the command line. If this is done, ftp will immediately attempt to establish a connection to an FTP server on that host; otherwise, it will enter its command interpreter and await instructions from the user. When ftp is awaiting commands from the user the prompt ‘ftp>’ is provided to the user. The following commands are recognized by ftp:
nmapsetting. File transfer uses the current settings for type, format, mode, and structure.
mgetcommands. When case is on (default is off), remote computer file names with all letters in upper case are written in the local directory with the letters mapped to lower case.
cris on (the default), carriage returns are stripped from this sequence to conform with the UNIX single linefeed record delimiter. Records on non-UNIX remote systems may contain single linefeeds; when an ASCII type transfer is made, these linefeeds may be distinguished from a record delimiter only when cr is off.
nmapsettings. The current settings for type, form, mode, and structure are used while transferring the file.
mput. If globbing is turned off with
glob, the file name arguments are taken literally and not expanded. Globbing for
mputis done as in csh. For
mget, each remote file name is expanded separately on the remote machine and the lists are not merged. Expansion of a directory name is likely to be different from expansion of the name of an ordinary file: the exact result depends on the foreign operating system and FTP server, and can be previewed by doing
mls remote-files -.
mput are not meant to transfer entire
directory subtrees of files. That can be done by transferring a
tar archive of the subtree (in binary mode).
dir, except multiple remote files may be specified. If interactive prompting is on, ftp will prompt the user to verify that the last argument is indeed the target local file for receiving
nmapsettings. Files are transferred into the local working directory, which can be changed with
lcd directory; new local directories can be created with
! mkdir directory.
nlist, except multiple remote files may be specified, and the local-file must be specified. If interactive prompting is on, ftp will prompt the user to verify that the last argument is indeed the target local file for receiving
nmap [inpattern outpattern
putcommands issued without a specified remote target filename. If arguments are specified, local filenames are mapped during
getcommands issued without a specified local target filename. This command is useful when connecting to a non-UNIX remote computer with different file naming conventions or practices.
The mapping follows the pattern set by inpattern and
outpattern. The template inpattern is used for incoming
filenames (which may have already been processed according to the
ntrans and case settings). Variable templating is accomplished
by including the sequences ‘$1’, ‘$2’, ..., ‘$9’ in
inpattern. Use ‘\’ to prevent this special treatment of
the ‘$’ character. All other characters are treated literally,
and are used to determine the
nmap inpattern variable
For example, given inpattern ‘$1.$2’ and the remote file name mydata.data, ‘$1’ would have the value ‘mydata’, and ‘$2’ would have the value ‘data’. The outpattern determines the resulting mapped filename. The sequences ‘$1’, ‘$2’, ...., ‘$9’ are replaced by any value resulting from the inpattern template. The sequence ‘$0’ is replaced by the original filename. Additionally, the sequence ‘[seq1, seq2]’ is replaced by seq1 if seq1 is not a null string; otherwise it is replaced by seq2. For example, the command
nmap $1.$2.$3 [$1,$2].[$2,file]
would yield the output filename myfile.data for input filenames myfile.data and myfile.data.old, myfile.file for the input filename myfile, and myfile.myfile for the input filename .myfile.
Spaces may be included in outpattern, as in the example:
nmap $1 sed "s/ *$//" > $1. Use the ‘\’ character to
prevent special treatment of the ‘$’, ‘[’, ‘]’, and
putcommands issued without a specified remote target filename. If arguments are specified, characters in local filenames are translated during
getcommands issued without a specified local target filename. This command is useful when connecting to a non-UNIX remote computer with different file naming conventions or practices.
Characters in a filename matching a character in inchars are
replaced with the corresponding character in outchars. If the
character's position in inchars is longer than the length of
outchars, the character is deleted from the file name.
autologinoption is on (default), ftp will also attempt to automatically log the user in to the FTP server.
PASVcommand for all data connections instead of the usual
PASVcommand requests that the remote server open a port for the data connection and return the address of that port. The remote server listens on that port and the client connects to it. When using the more traditional
PORTcommand, the client listens on a port and sends that address to the remote server, who connects back to it. Passive mode is useful when using ftp through a gateway router or host that controls the directionality of traffic. (Note that though ftp servers are required to support the
PASVcommand by RFC 1123, some do not.) If epsv4 has been set to on, the client will attempt
PASVfor IPv4. As a last resort
LPSVis attempted. With IPv6 only
mputwill transfer all files, and any
mdeletewill delete all files.
proxy ?to see other ftp commands executable on the secondary connection. The following commands behave differently when prefaced by
openwill not define new macros during the auto-login process,
closewill not erase existing macro definitions,
mgettransfer files from the host on the primary control connection to the host on the secondary control connection, and
appendtransfer files from the host on the secondary control connection to the host on the primary control connection. Third party file transfers depend upon support of the FTP protocol
PASVcommand by the server on the secondary control connection.
nmapsettings in naming the remote file. File transfer uses the current settings for type, format, mode, and structure.
get, except that if local-file exists and is smaller than remote-file, local-file is presumed to be a partially transferred copy of remote-file and the transfer is continued from the apparent point of failure. This command is useful when transferring very large files over networks that are prone to dropping connections.
putat the indicated marker. On UNIX systems, marker is usually a byte offset into the file.
mgetcommand, a ‘.1’ is appended to the name. If the resulting name matches another existing file, a ‘.2’ is appended to the original name. If this process continues up to ‘.99’, an error message is printed, and the transfer does not take place. The generated unique filename will be reported. Note that
runiquewill not affect local files generated from a shell command. The default value is off.
PORTcommands. By default, ftp will attempt to use a
PORTcommand when establishing a connection for each data transfer. The use of
PORTcommands can prevent delays when performing multiple file transfers. If the
PORTcommand fails, ftp will use the default data port. When the use of
PORTcommands is disabled, no attempt will be made to use
PORTcommands for each data transfer. This is useful for certain FTP implementations which do ignore
PORTcommands but, incorrectly, indicate they've been accepted.
STOUcommand for successful completion. The remote server will report unique name. Default value is off.
auto-logindisabled, this process is done automatically on initial connection to the FTP server.
Command arguments which have embedded spaces may be quoted with quote ‘"’ marks.
To abort a file transfer, use the terminal interrupt key (usually
C-c). Sending transfers will be immediately halted. Receiving
transfers will be halted by sending a FTP protocol ABOR command to the
remote server, and discarding any further data received. The speed at
which this is accomplished depends upon the remote server's support
ABOR processing. If the remote server does not support the
ABOR command, an ‘ftp>’ prompt will not appear until the
remote server has completed sending the requested file.
The terminal interrupt key sequence will be ignored when ftp
has completed any local processing and is awaiting a reply from the
remote server. A long delay in this mode may result from the
ABOR processing described above, or from unexpected behavior by
the remote server, including violations of the FTP protocol. If the
delay results from unexpected remote server behavior, the local
ftp program must be killed by hand.
Files specified as arguments to ftp commands are processed according to the following rules.
popenwith the argument supplied, and reads/writes from standard input/output. If the shell command includes spaces, the argument must be quoted; e.g. ‘"ls -lt"’. A particularly useful example of this mechanism is ‘dir more’.
globcommand. If the ftp command expects a single local file (e.g.
put), only the first filename generated by the globbing operation is used.
getcommands with unspecified local file names, the local filename is the remote filename, which may be altered by a
nmapsetting. The resulting filename may then be altered if
putcommands with unspecified remote file names, the remote filename is the local filename, which may be altered by a
nmapsetting. The resulting filename may then be altered by the remote server if
The FTP specification specifies many parameters which may affect a file transfer. The type may be one of ‘ascii’, ‘image’ (binary), ‘ebcdic’, and ‘local’ byte size (for PDP-10's and PDP-20's mostly). ftp supports the ‘ascii’ and ‘image’ types of file transfer, plus local byte size 8 for tenex mode transfers.
ftp supports only the default values for the remaining file
.netrc file contains login and initialization information
used by the auto-login process. It resides in the user's home
directory. The following tokens are recognized; they may be separated
by spaces, tabs, or new-lines:
default login anonymous password user@site
thereby giving the user automatic anonymous ftp login to machines not
specified in .netrc. This can be overridden by using the
-n flag to disable auto-login.
ACCTcommand if it does not.
macdefcommand functions. A macro is defined with the specified name; its contents begin with the next .netrc line and continue until a null line (consecutive new-line characters) is encountered. If a macro named init is defined, it is automatically executed as the last step in the auto-login process.
ftp utilizes the following environment variables.
Correct execution of many commands depends upon proper behavior by the remote server.
An error in the treatment of carriage returns in the 4.2BSD ascii-mode transfer code has been corrected. This correction may result in incorrect transfers of binary files to and from 4.2BSD servers using the ascii type. Avoid this problem by using the binary image type.
tftp is the user interface to the Internet TFTP, Trivial File Transfer Protocol, which allows users to transfer files to and from a remote machine. The remote host may be specified on the command line, in which case tftp uses host as the default host for future transfers.
tftp [option]... host
Once tftp is running, it issues the prompt and recognizes the following commands:
tftp> get [2001:1234::12]:issue
Because there is no user-login or validation within the tftp protocol, the remote site will probably have some sort of file-access restrictions in place. The exact methods are specific to each site and therefore difficult to document here.
rsh executes command on host and copies its standard input to the remote command, the standard output of the remote command to its standard output, and the standard error of the remote command to its standard error. Interrupt, quit and terminate signals are propagated to the remote command; rsh normally terminates when the remote command does.
When using the rsh command, you can create a link to your path using a host name as the link name. For example:
# ln -s /usr/bin/rsh hostname # hostname ls
hostname will be passed to rsh as the default host.
rsh allows access to the remote host without the use of a passwd. For details, See rcmd.
The options are as follows :
If no command is specified, you will be logged in on the remote host using rlogin.
Shell metacharacters which are not quoted are interpreted on the local machine, while quoted metacharacters are interpreted on the remote machine. For example:
rsh otherhost cat remotefile >> localfile rsh otherhost cat remotefile ">> "localfile
The first command appends the remote file file remotefile to the local file localfile, while the later command appends remotefile to other_remotefile.
rlogin command logs into a specified remote host and connects your local terminal to the remote host. The remote terminal type is the same as that given in the TERM local environment variable. The terminal or window size is also the same, if the remote host supports them, and any changes in size are transferred.
When using the rlogin command, you can create a link to your path using a host name as the link name. For example:
# ln -s /usr/bin/rlogin hostname # hostname -8
Using hostname automatically uses the rlogin to log in to the remote host named hostname.
rlogin allows access to the remote host without the use of a passwd. For details, See rcmd.
The options are as follows :
A line of the form escape-char. disconnects from the remote host. Similarly, the line escape-charC-Z will suspend the rlogin session, and escape-chardelayed-suspend-char suspends the send portion of the rlogin, but allows output from the remote system. By default, the tilde (‘~) character’ is the escape-char, and normally C-Y is the delayed-suspend-char.
All echoing takes place at the remote site, so that (except for delays) the rlogin is transparent. Flow control via C-S/C-Q, if supported, stop and start the flow of information, flushing of input and output on interrupts are handled properly.
On the server side the
are used to authenticate, see the appropriate man page for more
information, if supported.
If rlogin was compiled with kerberos support, options -x, -k, -K are available. Each user may have a private authorization list in the file .klogin in their home directory. Each line in this file should contain a Kerberos principal name of the form ‘principal.instance@realm’. If the originating user is authenticated to one of the principals named in .klogin, access is granted to the account. The principal ‘accountname.@localrealm’ is granted access if there is no .klogin file. Otherwise a login and password will be prompted for on the remote machine as in login. To avoid certain security problems, the .klogin file must be owned by the remote user. If Kerberos authentication fails, a warning message is printed and the standard Berkeley rlogin is used instead.
rcp copies files between machines. Each file or directory argument is either a remote file name of the form ‘rname@rhost:path’, or a local file name (containing no ‘:’ characters, or a ‘/’ before any ‘:’s).
rcp [option]... old-file new-file rcp [option]... files... directory
rcpto attempt to preserve (duplicate) in its copies the modification times and modes of the source files, ignoring the umask. By default, the mode and owner of file are preserved if it already existed; otherwise the mode of the source file modified by the
umaskfunction on the destination host is used.
rcp doesn't detect all cases where the target of a copy might be a file in cases where only a directory should be legal.
rcp can be confused by any output generated by commands in a .login, .profile, or .cshrc file on the remote host.
The destination user and hostname may have to be specified as ‘rhost.rname’ when the destination machine is running the 4.2BSD version of rcp.
rexec is a program that executes a program on another host.
rexec --user=login --password=pass --host=host \ [OPTION] command
The command line arguments are as follows:
talk is a visual communication program which copies lines from your terminal to that of another user.
The command line arguments are as follows:
When first called, talk sends the message:
Message from TalkDaemon@his_machine... talk: connection requested by your_name@your_machine. talk: respond with: talk your_name@your_machine
to the user you wish to talk to. At this point, the recipient of the message should reply by typing:
It doesn't matter from which machine the recipient replies, as long as his login-name is the same. Once communication is established, the two parties may type simultaneously, with their output appearing in separate windows. Typing C-L will cause the screen to be reprinted, while your erase, kill, and word kill characters will behave normally. To exit, just type your interrupt character; talk then moves the cursor to the bottom of the screen and restores the terminal to its previous state.
Permission to talk may be denied or granted by use of the mesg command. At the outset talking is allowed. Certain commands, in particular nroff and pr, disallow messages in order to prevent messy output.
To exit, just type your interrupt character; talk then moves the cursor to the bottom of the screen and restores the terminal to its previous state.
Login to a remote system HOST, optionally using a (non-standard) service port PORT:
telnet [OPTION...] [HOST [PORT]]
inetd program should be run at boot time by /etc/rc. It then listens for connections on certain internet sockets. When a connection is found on one of its sockets, it decides what service the socket corresponds to, and invokes a program to service the request. The server program is invoked with the service socket as its standard input, output and error descriptors. After the program is finished, inetd continues to listen on the socket (except in some cases which will be described below). Essentially, inetd allows running one daemon to invoke several others, reducing load on the system.
There are two types of services that inetd can start: standard and TCPMUX. A standard service has a well-known port assigned to it; it may be a service that implements an official Internet standard or is a BSD-specific service. As described in RFC 1078, TCPMUX services are nonstandard services that do not have a well-known port assigned to them. They are invoked from inetd when a program connects to the “tcpmux” well-known port and specifies the service name. This feature is useful for adding locally-developed servers.
Normally, inetd is invoked without any arguments. It does, however, support several command line options. These are:
Upon execution, inetd reads its configuration information from a configuration pathnames on the command line, by default, /etc/inetd.conf and /etc/initd.d. If the configuration pathname is a directory, all the files in the directory are read like a configuration file. All of the configuration files are read and merged. There must be an entry for each field in the configuration file, with entries for each field separated by a tab or a space. Comments are denoted by a “#” at the beginning of a line. There must be an entry for each field. The fields of the configuration file are summarized in the table below (optional parts are enclosed in square brackets:
Optional ‘service node’ prefix is allowed for internet services. When present, it supplies the local addresses inetd should use when listening for that service. ‘Service node’ consists of a comma-separated list of addresses. Both symbolic host names and numeric IP addresses are allowed. Symbolic hostnames are looked up in DNS service. If a hostname has multiple address mappings, inetd creates a socket to listen on each address.
To avoid repeating an address that occurs frequently, a line with a host address specifier and colon, but no further fields is allowed, e.g.:
The address specifier from such a line is remembered and used for all further lines lacking an explicit host specifier. Such a default address remains in effect until another such line or end of the configuration is encountered, whichever occurs first.
A special hostname ‘*’ stands for
INADDR_ANY. When used
in a normal configuration line, it causes the default address
specifier to be ignored for that line. When used in a default address
it causes any previous default address specifier to be forgotten.
Servers using stream sockets generally are multi-threaded and use the ‘nowait’ entry. Connection requests for these services are accepted by inetd, and the server is given only the newly-accepted socket connected to a client of the service. Most stream-based services and all TCPMUX services operate in this manner. For such services, the number of running instances of the server can be limitied by specifying optional ‘max’ suffix (a decimal number), e.g.: ‘nowait.15’.
Stream-based servers that use ‘wait’ are started with the
listening service socket, and must accept at least one connection
request before exiting. Such a server would normally accept and
process incoming connection requests until a timeout. services must
It is common usage to specify /usr/sbin/tcpd in this field.
argv, which is the name of the program. If the service is provided internally, this entry must contain the word ‘internal’, or be empty.
The inetd program provides several “trivial” services internally by use of routines within itself. All these services can operate both in ‘stream’ and in ‘dgram’ mode. They are:
The TCPMUX protocol.
A TCP client connects to a foreign host on TCP port 1. It sends the service name followed by a carriage-return line-feed <CRLF>. The service name is never case sensitive. The server replies with a single character indicating positive (+) or negative (-) acknowledgment, immediately followed by an optional message of explanation, terminated with a <CRLF>. If the reply was positive, the selected protocol begins; otherwise the connection is closed.” The program is passed the TCP connection as file descriptors 0 and 1.
If the TCPMUX service name begins with a “+”, inetd returns the positive reply for the program. This allows you to invoke programs that use stdin/stdout without putting any special server code in them.
The special service name ‘help’ causes inetd to list TCPMUX services in inetd.conf.
To define TCPMUX services, the configuration file must contain a ‘tcpmux internal’ definition.
Here are several example service entries for the various types of services:
ftp stream tcp nowait root /usr/libexec/ftpd ftpd -l ntalk dgram udp wait root /usr/libexec/ntalkd ntalkd tcpmux stream tcp nowait root internal tcpmux/+date stream tcp nowait guest /bin/date date tcpmux/phonebook stream tcp nowait guest /usr/bin/phonebook phonebook
If a connection is made with a streaming protocol (‘stream’) and if --environment option has been given, inetd will set the following environment variables before starting the program:
Additionally, if given the --remote option, inetd sets the following environment variables:
The inetd server logs error messages using syslog. Important error messages and their explanations are:
Use the -R option, as described above, to change the rate
limit. Once the limit is reached, the service will be reenabled
automatically in 10 minutes.
syslogd is a system service that provides error logging facility. Messages are read from the UNIX domain socket /dev/log, from an Internet domain socket specified in /etc/services, and from the special device /dev/klog (to read kernel messages).
syslogd creates the file /var/run/syslog.pid, and stores its process id there. This can be used to kill or reconfigure syslogd.
The message sent to syslogd should consist of a single line.
The message can contain a priority code, which should be a preceding
decimal number in angle braces, for example,
priority code should map into the priorities defined in the include
syslogd reads its configuration file when it starts up and whenever it receives a hangup signal. The syslog.conf file is the configuration file for the syslogd program. It consists of lines with two fields: the selector field which specifies the types of messages and priorities to which the line applies, and an action field which specifies the action to be taken if a message syslogd receives matches the selection criteria. The selector field is separated from the action field by one or more tab or space characters. A rule can be splitted in several lines if all lines except the last are terminated with a backslash ‘\’.
The Selectors function are encoded as a facility, a period (‘.’), and a level, with no intervening white-space. Both the facility and the level are case insensitive.
The facility describes the part of the system generating the message, and is one of the following keywords: ‘auth’, ‘authpriv’, ‘cron’, ‘daemon’, ‘kern’, ‘lpr’, ‘mail’, ‘mark’, ‘news’, ‘syslog’, ‘user’, ‘uucp’ and ‘local0’ through ‘local7’. These keywords (with the exception of ‘mark’) correspond to the similar ‘LOG_’ values specified to the ‘openlog’ and ‘syslog’ library routines. See Syslog, for details.
The level describes the severity of the message, and is a keyword from the following ordered list (higher to lower): ‘emerg’, ‘alert’, ‘crit’, ‘err, warning’, ‘notice’ and ‘debug’. These keywords correspond to the similar ‘LOG_’ values specified to the syslog library routine.
See syslog and vsyslog, for a further descriptions of both the facility and level keywords and their significance.
If a received message matches the specified facility and is of the specified level (or a higher level), the action specified in the action field will be taken.
Multiple selectors may be specified for a single action by separating them with semicolon (‘;’) characters. It is important to note, however, that each selector can modify the ones preceding it.
Multiple facilities may be specified for a single level by separating them with comma (‘,’) characters.
An asterisk (‘*’) can be used to specify all facilities or all levels. Two asterisks (‘**’) specifie all facilities not named previously in the configuration file.
By default, a level applies to all messages with the same or higher level. The equal (‘=’) character can be prepended to a level to restrict this line of the configuration file to messages with the very same level.
An exclamation mark (‘!’) prepended to a level or the asterisk means that this line of the configuration file does not apply to the specified level (and higher ones). In conjunction with the equal sign, you can exclude single levels as well.
The special facility ‘mark’ receives a message at priority ‘info’ every 20 minutes. This is not enabled by a facility field containing an asterisk.
The special level ‘none’ disables a particular facility.
The action field of each line specifies the action to be taken when the selector field selects a message. There are five forms:
You may prepend a minus (‘-’) to the path to omit syncing the file after each message log. This can cause data loss at system crashes, but increases performance for programs which use logging extensively.
Blank lines and lines whose first non-blank character is a hash (‘#’) character are ignored.
A configuration file might appear as follows:
# Log all kernel messages, authentication messages of # level notice or higher and anything of level err or # higher to the console. # Don't log private authentication messages! *.err;kern.*;auth.notice;authpriv.none /dev/console # Log anything (except mail) of level info or higher. # Don't log private authentication messages! *.info;mail.none;authpriv.none /var/log/messages # The authpriv file has restricted access. authpriv.* /var/log/secure # Log all the mail messages in one place. mail.* /var/log/maillog # Everybody gets emergency messages, plus log them on another # machine. *.emerg * *.emerg @arpa.berkeley.edu # Root and Eric get alert and higher messages. *.alert root,eric # Save mail and news errors of level err and higher in a # special file. uucp,news.crit /var/log/spoolerr
The effects of multiple selectors are sometimes not intuitive. For example ‘mail.crit,*.err’ will select the ‘mail’ facility messages at the level of ‘err’ or higher, not at the level of ‘crit’ or higher.
ftpd is the Internet File Transfer Protocol server process. The server uses the TCP protocol and listens at the port specified in the ‘ftp’ service specification.
Anonymous logins will continue to work when this option is used.
syslogusing facility ‘LOG_FTP’.
syslogwith a facility of ‘LOG_FTP’. If this option is specified twice, the retrieve (
get), store (
put), append, delete, make directory, remove directory and rename operations and their filename arguments are also logged.
The file /etc/nologin can be used to disable ftp access. If the file exists, ftpd displays it and exits. If the file /etc/ftpwelcome exists, ftpd prints it before issuing the ‘ready’ message. If the file /etc/motd exists, ftpd prints it after a successful login.
The FTP server currently supports the following FTP requests. The case of the requests is ignored.
|ABOR||abort previous command
|ACCT||specify account (ignored)
|ALLO||allocate storage (vacuously)
|APPE||append to a file
|CDUP||change to parent of current working directory
|CWD||change working directory
|DELE||delete a file
|HELP||give help information
|LIST||give list files in a directory (“ls -lgA”)
|MKD||make a directory
|MDTM||show last modification time of file
|MODE||specify data transfer mode
|NLST||give name list of files in directory
|PASV||prepare for server-to-server transfer
|PORT||specify data connection port
|PWD||print the current working directory
|REST||restart incomplete transfer
|RETR||retrieve a file
|RMD||remove a directory
|RNFR||specify rename-from file name
|RNTO||specify rename-to file name
|SIZE||return size of file
|STAT||return status of server
|STOR||store a file
|STOU||store a file with a unique name
|STRU||specify data transfer structure
|SYST||show operating system type of server system
|TYPE||specify data transfer type
|USER||specify user name
|XCUP||change to parent of current working directory (deprecated)
|XCWD||change working directory (deprecated)
|XMKD||make a directory (deprecated)
|XPWD||print the current working directory (deprecated)
|XRMD||remove a directory (deprecated)
The following non-standard or UNIX specific commands are supported by
|UMASK||change umask, e.g. |
|IDLE||set idle-timer, e.g. |
|CHMOD||change mode of a file, e.g. |
|HELP||give help information.
The remaining FTP requests specified in RFC 959 are recognized, but
SIZE are not specified in RFC
959, but will appear in the next updated FTP RFC.
The ftp server will abort an active file transfer only when the
ABOR command is preceded by a Telnet ‘Interrupt Process’
(IP) signal and a Telnet ‘Synch’ signal in the command Telnet
stream, as described in Internet RFC 959. If a
STAT command is
received during a data transfer, preceded by a Telnet IP and Synch,
transfer status will be returned.
ftpd interprets file names according to the globbing
conventions used by csh. This allows users to utilize the
ftpd authenticates users according to three rules.
In the last case, ftpd takes special measures to restrict the client's access privileges. The server performs a chroot to the home directory of the ‘ftp’ user. In order that system security is not breached, it is recommended that the ‘ftp’ subtree be constructed with care, following these rules:
The rshd server is the server for the
and, consequently, for the rsh (see rsh invocation)
program. The server provides remote execution facilities with
authentication based on privileged port numbers from trusted hosts.
The rshd server listens for service requests at the port
indicated in the ‘cmd’ service specification. When a service
request is received the following protocol is initiated:
ruserok, which uses the file /etc/hosts.equiv and the .rhosts file found in the user's home directory. The -l option prevents
ruserokfrom doing any validation based on the user's .rhosts file, unless the user is the superuser.
See ruserok, for details.
The options are as follows:
Except for the last one listed below, all diagnostic messages are returned on the initial socket, after which any network connections are closed. An error is indicated by a leading byte with a value of 1 (0 is returned in step 10 above upon successful completion of all the steps prior to the execution of the login shell).
The authentication procedure used here assumes the integrity of each client machine and the connecting medium. This is insecure, but is useful in an “open” environment.
rlogind is the server for the rlogin program (see rlogin invocation). The server provides a remote login facility with authentication based on privileged port numbers from trusted hosts.
rlogind listens for service requests at the port indicated in the ‘login’ service specification. When a service request is received the following protocol is initiated:
Once the source port and address have been checked, rlogind proceeds with the authentication process described rshd invocation. It then allocates a pseudo terminal, and manipulates file descriptors so that the slave half of the pseudo terminal becomes the stdin, stdout, and stderr for a login process. The login process is an instance of the login program, invoked with the -f option if authentication has succeeded. If automatic authentication fails, the user is prompted to log in as if on a standard terminal line.
The parent of the login process manipulates the master side of the pseudo terminal, operating as an intermediary between the login process and the client instance of the rlogin program. In normal operation, the packet protocol described in ‘PTY’ is invoked to provide C-S/C-Q type facilities and propagate interrupt signals to the remote programs. The login process propagates the client terminal's baud rate and terminal type, as found in the environment variable, TERM. The screen or window size of the terminal is requested from the client, and window size changes from the client are propagated to the pseudo terminal.
Transport-level keepalive messages are enabled unless the -n
option is client instance of the
rlogin program. The use of
keepalive messages allows sessions to be timed out if the client
crashes or becomes unreachable.
See ruserok, for details.
The options are as follows:
All initial diagnostic messages are indicated by a leading byte with a value of 1, after which any network connections are closed. If there are no errors before login is invoked, a null byte is returned as in indication of success.
The authentication procedure used here assumes the integrity of each client machine and the connecting medium. This is insecure, but is useful in an “open” environment.
rexecd is the server for the
Rexec routine. The
server provides remote execution facilities with authentication based
on user names and passwords.
rexecd listens for service requests at the port indicated in the ‘exec’ service specification. When a service request is received the following protocol is initiated:
Except for the last one listed below, all diagnostic messages are returned on the initial socket, after which any network connections are closed. An error is indicated by a leading byte with a value of 1 (0 is returned in step 7 above upon successful completion of all the steps prior to the command execution).
Note, that indicating ‘Login incorrect’ as opposed to ‘Password incorrect’ is a security breach which allows people to probe a system for users with null passwords.
talkd is the server that notifies a user that someone else wants to initiate a conversation. It acts as a repository of invitations, responding to requests by clients wishing to rendezvous to hold a conversation.
In normal operation, a client, the caller, initiates a rendezvous by
CTL_MSG to the server of type ‘LOOK_UP’ (see
protocols/talkd.h). This causes the server to search its
invitation tables to check if an invitation currently exists for the
caller (to speak to the callee specified in the message). If the
lookup fails, the caller then sends an ‘ANNOUNCE’ message causing
the server to broadcast an announcement on the callee's login ports
requesting contact. When the callee responds, the local server uses
the recorded invitation to respond with the appropriate rendezvous
address and the caller and callee client programs establish a stream
connection through which the conversation takes place.
There is one additional category ‘tcp’, that does not allow the additional level indicator, but is instead equivalent to setting the socket option ‘SO_DEBUG’ for debugging the complete traffic.
The outcome is the file /tmp/telnet.debug, to which
data is incrementally added as time passes.
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--: Common options
--8-bit: rlogin invocation
--acl: talkd invocation
--active: ftp invocation
--address: ping invocation
--aliases: hostname invocation
--allow-root: rlogind invocation
--anonymous-only: ftpd invocation
--auth: ftpd invocation
--bind: syslogd invocation
--count: ping invocation
--d: talkd invocation
--daemon: rlogind invocation
--daemon: ftpd invocation
--debug: talkd invocation
--debug: ftpd invocation
--debug: syslogd invocation
--debug: rlogin invocation
--debug: rsh invocation
--debug: ftp invocation
--debug: ping invocation
--domain: hostname invocation
--echo: ping invocation
--encrypt: rlogind invocation
--encrypt: rshd invocation
--encrypt: rcp invocation
--encrypt: rlogin invocation
--encrypt: rsh invocation
--escape: rlogin invocation
--file: logger invocation
--file: hostname invocation
--flood: ping invocation
--fqdn: hostname invocation
--help: Common options
--hop: syslogd invocation
--host: logger invocation
--id: logger invocation
--idle-timeout: talkd invocation
--ignore-routing-log: ping invocation
--inet: syslogd invocation
--interval: ping invocation
--ip-addresses: hostname invocation
--ipany: syslogd invocation
--ipv4: syslogd invocation
--ipv4: ftp invocation
--ipv4: logger invocation
--ipv6: syslogd invocation
--ipv6: ftp invocation
--ipv6: logger invocation
--kerberos: rlogind invocation
--kerberos: rshd invocation
--kerberos: rcp invocation
--kerberos: rlogin invocation
--kerberos: rsh invocation
--linger: ping invocation
--local-domain: rlogind invocation
--local-domain: rshd invocation
--logging: ftpd invocation
--long: hostname invocation
--mark: syslogd invocation
--max-timeout: ftpd invocation
--nis: hostname invocation
--no-detach: syslogd invocation
--no-escape: rlogin invocation
--no-forward: syslogd invocation
--no-glob: ftp invocation
--no-keepalive: rlogind invocation
--no-keepalive: rshd invocation
--no-klog: syslogd invocation
--no-login: ftp invocation
--no-prompt: ftp invocation
--no-rhosts: rlogind invocation
--no-rhosts: rshd invocation
--no-unixaf: syslogd invocation
--no-version: ftpd invocation
--numeric: ping invocation
--passive: ftp invocation
--pattern: ping invocation
--pidfile: ftpd invocation
--pidfile: syslogd invocation
--port: rlogind invocation
--port: traceroute invocation
--preload: ping invocation
--preserve: rcp invocation
--priority: logger invocation
--prompt: ftp invocation
--rcfile: syslogd invocation
--realm: rcp invocation
--realm: rlogin invocation
--realm: rsh invocation
--recursive: rcp invocation
--request-ttl: talkd invocation
--resolve-hostnames: traceroute invocation
--reverse-required: rlogind invocation
--route: ping invocation
--short: hostname invocation
--size: ping invocation
--socket: syslogd invocation
--source: logger invocation
--stderr: logger invocation
--tag: logger invocation
--timeout: talkd invocation
--timeout: ftpd invocation
--timeout: ping invocation
--timestamp: ping invocation
--trace: ftp invocation
--tries: traceroute invocation
--type: traceroute invocation
--type: ping invocation
--umask: ftpd invocation
--usage: Common options
--user: rsh invocation
--verify-hostname: rlogind invocation
--verify-hostname: rshd invocation
--version: Common options
--yp: hostname invocation
-4: syslogd invocation
-4: ftp invocation
-4: logger invocation
-6: syslogd invocation
-6: ftp invocation
-6: logger invocation
-8: rlogin invocation
-a: talkd invocation
-a: rlogind invocation
-a: rshd invocation
-a: ftpd invocation
-A: ftpd invocation
-A: ftp invocation
-a: hostname invocation
-b: syslogd invocation
-c: ping invocation
-D: rlogind invocation
-d: rlogind invocation
-D: rshd invocation
-d: ftpd invocation
-D: ftpd invocation
-d: syslogd invocation
-d: rlogin invocation
-d: rsh invocation
-d: ftp invocation
-d: ping invocation
-d: hostname invocation
-debug: rlogind invocation
-debug: rshd invocation
-e: rlogin invocation
-E: rlogin invocation
-f: syslogd invocation
-f: ping invocation
-f: logger invocation
-F: hostname invocation
-f: hostname invocation
-g: ftp invocation
-h: syslogd invocation
-h: logger invocation
-i: talkd invocation
-i: ftp invocation
-i: ping invocation
-i: logger invocation
-i: hostname invocation
-k: rlogind invocation
-k: rshd invocation
-k: rcp invocation
-K: rcp invocation
-k: rlogin invocation
-K: rlogin invocation
-k: rsh invocation
-K: rsh invocation
-L: rlogind invocation
-l: rlogind invocation
-L: rshd invocation
-l: rshd invocation
-l: ftpd invocation
-l: syslogd invocation
-l: rsh invocation
-l: ping invocation
-m: syslogd invocation
-M: traceroute invocation
-n: rlogind invocation
-n: rshd invocation
-n: syslogd invocation
-n: ftp invocation
-n: ping invocation
-o: rlogind invocation
-p: rlogind invocation
-p: ftpd invocation
-p: syslogd invocation
-p: rcp invocation
-p: ftp invocation
-p: traceroute invocation
-p: ping invocation
-p: logger invocation
-q: ftpd invocation
-q: traceroute invocation
-r: talkd invocation
-r: rlogind invocation
-r: syslogd invocation
-r: rcp invocation
-R: ping invocation
-r: ping invocation
-s: syslogd invocation
-s: ping invocation
-s: logger invocation
-S: logger invocation
-s: hostname invocation
-t: talkd invocation
-t: ftpd invocation
-T: ftpd invocation
-t: ftp invocation
-t: ping invocation
-t: logger invocation
-u: ftpd invocation
-W: ping invocation
-w: ping invocation
-x: rlogind invocation
-x: rshd invocation
-x: rcp invocation
-x: rlogin invocation
-x: rsh invocation
-y: hostname invocation
traceroute: traceroute invocation