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Section (1) login

Linux manual pages Section 1  

Name

login — begin session on the system

Synopsis

login [−p] [ −h host ] [−H] [ −f username | username ]

DESCRIPTION

login is used when signing onto a system. If no argument is given, login prompts for the username.

The user is then prompted for a password, where appropriate. Echoing is disabled to prevent revealing the password. Only a small number of password failures are permitted before login exits and the communications link is severed.

If password aging has been enabled for the account, the user may be prompted for a new password before proceeding. He will be forced to provide his old password and the new password before continuing. Please refer to passwd(1) for more information.

The user and group ID will be set according to their values in the /etc/passwd file. There is one exception if the user ID is zero: in this case, only the primary group ID of the account is set. This should allow the system administrator to login even in case of network problems. The value for $HOME, $USER, $SHELL, $PATH, $LOGNAME, and $MAIL are set according to the appropriate fields in the password entry. $PATH defaults to /usr/local/bin:/bin:/usr/bin for normal users, and to /usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin for root, if not otherwise configured.

The environment variable $TERM will be preserved, if it exists (other environment variables are preserved if the −p option is given), else it will be initialized to the terminal type on your tty.

Then the user_zsingle_quotesz_s shell is started. If no shell is specified for the user in /etc/passwd, then /bin/sh is used. If there is no directory specified in /etc/passwd, then / is used (the home directory is checked for the .hushlogin file described below).

If the file .hushlogin exists, then a quiet login is performed (this disables the checking of mail and the printing of the last login time and message of the day). Otherwise, if /var/log/lastlog exists, the last login time is printed (and the current login is recorded).

OPTIONS

−p

Used by getty(8) to tell login not to destroy the environment.

−f

Used to skip a second login authentication. This specifically does not work for root, and does not appear to work well under Linux.

−h

Used by other servers (i.e., telnetd(8)) to pass the name of the remote host to login so that it may be placed in utmp and wtmp. Only the superuser may use this option.

Note that the −h option has impact on the PAM service name. The standard service name is login, with the −h option the name is remote. It is necessary to create proper PAM config files (e.g. /etc/pam.d/login and /etc/pam.d/remote).

−H

Used by other servers (i.e., telnetd(8)) to tell login that printing the hostname should be suppressed in the login: prompt. See also LOGIN_PLAIN_PROMPT below if your server does not allow to configure login command line.

−−help

Display help text and exit.

−V, −−version

Display version information and exit.

CONFIG FILE ITEMS

login reads the /etc/login.defs(5) configuration file. Note that the configuration file could be distributed with another package (e.g. shadow-utils). The following configuration items are relevant for login(1):

MOTD_FILE (string)

If defined, a : delimited list of message of the day files to be displayed upon login. The default value is /etc/motd. If the MOTD_FILE item is empty or a quiet login is enabled, then the message of the day is not displayed. Note that the same functionality is also provided by pam_motd(8) PAM module.

LOGIN_PLAIN_PROMPT (boolean)

Tell login that printing the hostname should be suppressed in the login: prompt. This is alternative to the −H command line option. The default value is no.

LOGIN_TIMEOUT (number)

Max time in seconds for login. The default value is 60.

LOGIN_RETRIES (number)

Maximum number of login retries in case of a bad password. The default value is 3.

FAIL_DELAY (number)

Delay in seconds before being allowed another three tries after a login failure. The default value is 5.

TTYPERM (string)

The terminal permissions. The default value is 0600 or 0620 if tty group is used.

TTYGROUP (string)

The login tty will be owned by the TTYGROUP. The default value is tty. If the TTYGROUP does not exist, then the ownership of the terminal is set to the user_zsingle_quotesz_s primary group.

The TTYGROUP can be either the name of a group or a numeric group identifier.

HUSHLOGIN_FILE (string)

If defined, this file can inhibit all the usual chatter during the login sequence. If a full pathname (e.g. /etc/hushlogins) is specified, then hushed mode will be enabled if the user_zsingle_quotesz_s name or shell are found in the file. If this global hush login file is empty then the hushed mode will be enabled for all users.

If a full pathname is not specified, then hushed mode will be enabled if the file exists in the user_zsingle_quotesz_s home directory.

The default is to check /etc/hushlogins and if it does not exist then ~/.hushlogin

If the HUSHLOGIN_FILE item is empty, then all the checks are disabled.

DEFAULT_HOME (boolean)

Indicate if login is allowed if we cannot change directory to the home directory. If set to yes, the user will login in the root (/) directory if it is not possible to change directory to her home. The default value is yes.

LOG_UNKFAIL_ENAB (boolean)

Enable display of unknown usernames when login failures are recorded. The default value is no.

Note that logging unknown usernames may be a security issue if a user enters her password instead of her login name.

ENV_PATH (string)

If set, it will be used to define the PATH environment variable when a regular user logs in. The default value is /usr/local/bin:/bin:/usr/bin

ENV_ROOTPATH (string)

ENV_SUPATH (string)

If set, it will be used to define the PATH environment variable when the superuser logs in. The default value is /usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

FILES

/var/run/utmp
/var/log/wtmp
/var/log/lastlog
/var/spool/mail/*
/etc/motd
/etc/passwd
/etc/nologin
/etc/pam.d/login
/etc/pam.d/remote
/etc/hushlogins
.hushlogin

SEE ALSO

mail(1), passwd(1), passwd(5), environ(7), getty(8), init(8), shutdown(8)

BUGS

The undocumented BSD −r option is not supported. This may be required by some rlogind(8) programs.

A recursive login, as used to be possible in the good old days, no longer works; for most purposes su(1) is a satisfactory substitute. Indeed, for security reasons, login does a vhangup() system call to remove any possible listening processes on the tty. This is to avoid password sniffing. If one uses the command login, then the surrounding shell gets killed by vhangup() because it_zsingle_quotesz_s no longer the true owner of the tty. This can be avoided by using exec login in a top-level shell or xterm.

AUTHOR

Derived from BSD login 5.40 (5/9/89) by Michael Glad for HP-UX

Ported to Linux 0.12: Peter Orbaek

Rewritten to a PAM-only version by Karel Zak

AVAILABILITY

The login command is part of the util-linux package and is available from Linux Kernel Archive


  Copyright 1993 Rickard E. Faith (faithcs.unc.edu)
May be distributed under the GNU General Public License

Section (3) login

Linux manual pages Section 3  

Name

login, logout — write utmp and wtmp entries

Synopsis

#include <utmp.h>
void login( const struct utmp *ut);
 
int logout( const char *ut_line);
 
[Note] Note

Link with −lutil.

DESCRIPTION

The utmp file records who is currently using the system. The wtmp file records all logins and logouts. See utmp(5).

The function login() takes the supplied struct utmp, ut, and writes it to both the utmp and the wtmp file.

The function logout() clears the entry in the utmp file again.

GNU details

More precisely, login() takes the argument ut struct, fills the field ut−>ut_type (if there is such a field) with the value USER_PROCESS, and fills the field ut−>ut_pid (if there is such a field) with the process ID of the calling process. Then it tries to fill the field ut−>ut_line. It takes the first of stdin, stdout, stderr that is a terminal, and stores the corresponding pathname minus a possible leading /dev/ into this field, and then writes the struct to the utmp file. On the other hand, if no terminal name was found, this field is filled with ??? and the struct is not written to the utmp file. After this, the struct is written to the wtmp file.

The logout() function searches the utmp file for an entry matching the ut_line argument. If a record is found, it is updated by zeroing out the ut_name and ut_host fields, updating the ut_tv timestamp field and setting ut_type (if there is such a field) to DEAD_PROCESS.

RETURN VALUE

The logout() function returns 1 if the entry was successfully written to the database, or 0 if an error occurred.

FILES

/var/run/utmp

user accounting database, configured through _PATH_UTMP in <paths.h>

/var/log/wtmp

user accounting log file, configured through _PATH_WTMP in <paths.h>

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value

login(),

logout()

 Thread safety

MT-Unsafe race:utent

sig:ALRM timer

In the above table, utent in race:utent signifies that if any of the functions setutent(3), getutent(3), or endutent(3) are used in parallel in different threads of a program, then data races could occur. login() and logout() calls those functions, so we use race:utent to remind users.

CONFORMING TO

Not in POSIX.1. Present on the BSDs.

NOTES

Note that the member ut_user of struct utmp is called ut_name in BSD. Therefore, ut_name is defined as an alias for ut_user in <utmp.h>

SEE ALSO

getutent(3), utmp(5)

COLOPHON

This page is part of release 4.16 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man−pages/.


  Derived from text written by Martin Schulze (or taken from glibc.info)
and text written by Paul Thompson - both copyright 2002.

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