Content-type: text/html; charset=UTF-8 Man page of LOGIN

LOGIN

Section: User Commands (1)
Updated: 03/14/2022
Index Return to Main Contents

NAME

SYNOPSIS

login [-p] [-h host] [username] [ENV=VAR...]
login [-p] [-h host] -f username
login [-p] -r host

DESCRIPTION

The login program is used to establish a new session with the system. It is normally invoked automatically by responding to the login: prompt on the user's terminal. login may be special to the shell and may not be invoked as a sub-process. When called from a shell, login should be executed as exec login which will cause the user to exit from the current shell (and thus will prevent the new logged in user to return to the session of the caller). Attempting to execute login from any shell but the login shell will produce an error message.

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 your account, you may be prompted for a new password before proceeding. You will be forced to provide your old password and the new password before continuing. Please refer to passwd(1) for more information.

Your user and group ID will be set according to their values in the /etc/passwd file. The value for $HOME, $SHELL, $PATH, $LOGNAME, and $MAIL are set according to the appropriate fields in the password entry. Ulimit, umask and nice values may also be set according to entries in the GECOS field.

On some installations, the environmental variable $TERM will be initialized to the terminal type on your tty line, as specified in /etc/ttytype.

An initialization script for your command interpreter may also be executed. Please see the appropriate manual section for more information on this function.

A subsystem login is indicated by the presence of a "*" as the first character of the login shell. The given home directory will be used as the root of a new file system which the user is actually logged into.

The login program is NOT responsible for removing users from the utmp file. It is the responsibility of getty(8) and init(8) to clean up apparent ownership of a terminal session. If you use login from the shell prompt without exec, the user you use will continue to appear to be logged in even after you log out of the "subsession".

OPTIONS

-f

: Do not perform authentication, user is preauthenticated.
Note: In that case, username is mandatory.

-h

: Name of the remote host for this login.

-p

: Preserve environment.

-r

: Perform autologin protocol for rlogin.

The -r, -h and -f options are only used when login is invoked by root.

CAVEATS

This version of login has many compilation options, only some of which may be in use at any particular site.

The location of files is subject to differences in system configuration.

As with any program, login's appearance can be faked. If non-trusted users have physical access to a machine, an attacker could use this to obtain the password of the next person coming to sit in front of the machine. Under Linux, the SAK mechanism can be used by users to initiate a trusted path and prevent this kind of attack.

CONFIGURATION

The following configuration variables in /etc/login.defs change the behavior of this tool:

CONSOLE_GROUPS (string)

: List of groups to add to the user's supplementary groups set when logging in on the console (as determined by the CONSOLE setting). Default is none.
Use with caution - it is possible for users to gain permanent access to these groups, even when not logged in on the console.

DEFAULT_HOME (boolean)

: Indicate if login is allowed if we can't cd to the home directory. Default is no.
If set to yes, the user will login in the root (/) directory if it is not possible to cd to her home directory.

ENV_PATH (string)

: If set, it will be used to define the PATH environment variable when a regular user login. The value is a colon separated list of paths (for example /bin:/usr/bin) and can be preceded by PATH=. The default value is PATH=/bin:/usr/bin.

ENV_SUPATH (string)

: If set, it will be used to define the PATH environment variable when the superuser login. The value is a colon separated list of paths (for example /sbin:/bin:/usr/sbin:/usr/bin) and can be preceded by PATH=. The default value is PATH=/sbin:/bin:/usr/sbin:/usr/bin.

ERASECHAR (number)

: Terminal ERASE character (010 = backspace, 0177 = DEL).
The value can be prefixed "0" for an octal value, or "0x" for an hexadecimal value.

FAIL_DELAY (number)

: Delay in seconds before being allowed another attempt after a login failure.

FAKE_SHELL (string)

: If set, login will execute this shell instead of the users' shell specified in /etc/passwd.

HUSHLOGIN_FILE (string)

: If defined, this file can inhibit all the usual chatter during the login sequence. If a full pathname is specified, then hushed mode will be enabled if the user's name or shell are found in the file. If not a full pathname, then hushed mode will be enabled if the file exists in the user's home directory.

KILLCHAR (number)

: Terminal KILL character (025 = CTRL/U).
The value can be prefixed "0" for an octal value, or "0x" for an hexadecimal value.

LOGIN_RETRIES (number)

: Maximum number of login retries in case of bad password.
This will most likely be overridden by PAM, since the default pam_unix module has its own built in of 3 retries. However, this is a safe fallback in case you are using an authentication module that does not enforce PAM_MAXTRIES.

LOGIN_TIMEOUT (number)

: Max time in seconds for login.

LOG_OK_LOGINS (boolean)

: Enable logging of successful logins.

LOG_UNKFAIL_ENAB (boolean)

: Enable display of unknown usernames when login failures are recorded.
Note: logging unknown usernames may be a security issue if an user enter her password instead of her login name.

TTYGROUP (string), TTYPERM (string)

The terminal permissions: the login tty will be owned by the TTYGROUP group, and the permissions will be set to TTYPERM.

By default, the ownership of the terminal is set to the user's primary group and the permissions are set to 0600.

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

If you have a write program which is "setgid" to a special group which owns the terminals, define TTYGROUP to the group number and TTYPERM to 0620. Otherwise leave TTYGROUP commented out and assign TTYPERM to either 622 or 600.

TTYTYPE_FILE (string)

: If defined, file which maps tty line to TERM environment parameter. Each line of the file is in a format something like "vt100 tty01".

USERGROUPS_ENAB (boolean)

: If set to yes, userdel will remove the user's group if it contains no more members, and useradd will create by default a group with the name of the user.

FILES

/var/run/utmp

: List of current login sessions.

/var/log/wtmp

: List of previous login sessions.

/etc/passwd

: User account information.

/etc/shadow

: Secure user account information.

/etc/motd

: System message of the day file.

/etc/nologin

: Prevent non-root users from logging in.

/etc/ttytype

: List of terminal types.

$HOME/.hushlogin

: Suppress printing of system messages.

/etc/login.defs

: Shadow password suite configuration.

This document was created by man2html, using the manual pages.
Time: 04:45:26 GMT, September 16, 2022 Content-type: text/html; charset=UTF-8 Man page of LOGIN

LOGIN

Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
Index Return to Main Contents

NAME

SYNOPSIS

#include <utmp.h>

void login(const struct utmp *ut);

int logout(const char *ut_line);

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>.

COLOPHON

This page is part of release 4.15 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/.

Index

NAME

SYNOPSIS

DESCRIPTION

GNU details

This document was created by man2html, using the manual pages.
Time: 04:45:48 GMT, September 16, 2022 Content-type: text/html; charset=UTF-8 Man page of LOGIN.DEFS

LOGIN.DEFS

Section: File Formats and Conversions (5)
Updated: 03/14/2022
Index Return to Main Contents

NAME

DESCRIPTION

The /etc/login.defs file defines the site-specific configuration for the shadow password suite. This file is required. Absence of this file will not prevent system operation, but will probably result in undesirable operation.

This file is a readable text file, each line of the file describing one configuration parameter. The lines consist of a configuration name and value, separated by whitespace. Blank lines and comment lines are ignored. Comments are introduced with a "#" pound sign and the pound sign must be the first non-white character of the line.

Parameter values may be of four types: strings, booleans, numbers, and long numbers. A string is comprised of any printable characters. A boolean should be either the value yes or no. An undefined boolean parameter or one with a value other than these will be given a no value. Numbers (both regular and long) may be either decimal values, octal values (precede the value with 0) or hexadecimal values (precede the value with 0x). The maximum value of the regular and long numeric parameters is machine-dependent.

The following configuration items are provided:

CHFN_RESTRICT (string)

: This parameter specifies which values in the gecos field of the /etc/passwd file may be changed by regular users using the chfn program. It can be any combination of letters f, r, w, h, for Full name, Room number, Work phone, and Home phone, respectively. For backward compatibility, yes is equivalent to rwh and no is equivalent to frwh. If not specified, only the superuser can make any changes. The most restrictive setting is better achieved by not installing chfn SUID.

CONSOLE_GROUPS (string)

: List of groups to add to the user's supplementary groups set when logging in on the console (as determined by the CONSOLE setting). Default is none.
Use with caution - it is possible for users to gain permanent access to these groups, even when not logged in on the console.

CREATE_HOME (boolean)

: Indicate if a home directory should be created by default for new users.
This setting does not apply to system users, and can be overridden on the command line.

DEFAULT_HOME (boolean)

: Indicate if login is allowed if we can't cd to the home directory. Default is no.
If set to yes, the user will login in the root (/) directory if it is not possible to cd to her home directory.

ENCRYPT_METHOD (string)

This defines the system default encryption algorithm for encrypting passwords (if no algorithm are specified on the command line).

It can take one of these values: DES (default), MD5, SHA256, SHA512.

Note: this parameter overrides the MD5_CRYPT_ENAB variable.

Note: This only affect the generation of group passwords. The generation of user passwords is done by PAM and subject to the PAM configuration. It is recommended to set this variable consistently with the PAM configuration.

ENV_HZ (string)

: If set, it will be used to define the HZ environment variable when a user login. The value must be preceded by HZ=. A common value on Linux is HZ=100.
The HZ environment variable is only set when the user (the superuser) logs in with sulogin.

ENV_PATH (string)

: If set, it will be used to define the PATH environment variable when a regular user login. The value is a colon separated list of paths (for example /bin:/usr/bin) and can be preceded by PATH=. The default value is PATH=/bin:/usr/bin.

ENV_SUPATH (string)

: If set, it will be used to define the PATH environment variable when the superuser login. The value is a colon separated list of paths (for example /sbin:/bin:/usr/sbin:/usr/bin) and can be preceded by PATH=. The default value is PATH=/sbin:/bin:/usr/sbin:/usr/bin.

ERASECHAR (number)

: Terminal ERASE character (010 = backspace, 0177 = DEL).
The value can be prefixed "0" for an octal value, or "0x" for an hexadecimal value.

FAIL_DELAY (number)

: Delay in seconds before being allowed another attempt after a login failure.

FAKE_SHELL (string)

: If set, login will execute this shell instead of the users' shell specified in /etc/passwd.

GID_MAX (number), GID_MIN (number)

: Range of group IDs used for the creation of regular groups by useradd, groupadd, or newusers.
The default value for GID_MIN (resp. GID_MAX) is 1000 (resp. 60000).

HUSHLOGIN_FILE (string)

: If defined, this file can inhibit all the usual chatter during the login sequence. If a full pathname is specified, then hushed mode will be enabled if the user's name or shell are found in the file. If not a full pathname, then hushed mode will be enabled if the file exists in the user's home directory.

KILLCHAR (number)

: Terminal KILL character (025 = CTRL/U).
The value can be prefixed "0" for an octal value, or "0x" for an hexadecimal value.

LOG_OK_LOGINS (boolean)

: Enable logging of successful logins.

LOG_UNKFAIL_ENAB (boolean)

: Enable display of unknown usernames when login failures are recorded.
Note: logging unknown usernames may be a security issue if an user enter her password instead of her login name.

LOGIN_RETRIES (number)

: Maximum number of login retries in case of bad password.
This will most likely be overridden by PAM, since the default pam_unix module has its own built in of 3 retries. However, this is a safe fallback in case you are using an authentication module that does not enforce PAM_MAXTRIES.

LOGIN_TIMEOUT (number)

: Max time in seconds for login.

MAIL_DIR (string)

: The mail spool directory. This is needed to manipulate the mailbox when its corresponding user account is modified or deleted. If not specified, a compile-time default is used.

MAIL_FILE (string)

: Defines the location of the users mail spool files relatively to their home directory.

The MAIL_DIR and MAIL_FILE variables are used by useradd, usermod, and userdel to create, move, or delete the user's mail spool.

MAX_MEMBERS_PER_GROUP (number)

Maximum members per group entry. When the maximum is reached, a new group entry (line) is started in /etc/group (with the same name, same password, and same GID).

The default value is 0, meaning that there are no limits in the number of members in a group.

This feature (split group) permits to limit the length of lines in the group file. This is useful to make sure that lines for NIS groups are not larger than 1024 characters.

If you need to enforce such limit, you can use 25.

Note: split groups may not be supported by all tools (even in the Shadow toolsuite). You should not use this variable unless you really need it.

MD5_CRYPT_ENAB (boolean)

Indicate if passwords must be encrypted using the MD5-based algorithm. If set to yes, new passwords will be encrypted using the MD5-based algorithm compatible with the one used by recent releases of FreeBSD. It supports passwords of unlimited length and longer salt strings. Set to no if you need to copy encrypted passwords to other systems which don't understand the new algorithm. Default is no.

This variable is superseded by the ENCRYPT_METHOD variable or by any command line option used to configure the encryption algorithm.

This variable is deprecated. You should use ENCRYPT_METHOD.

PASS_MAX_DAYS (number)

: The maximum number of days a password may be used. If the password is older than this, a password change will be forced. If not specified, -1 will be assumed (which disables the restriction).

PASS_MIN_DAYS (number)

: The minimum number of days allowed between password changes. Any password changes attempted sooner than this will be rejected. If not specified, -1 will be assumed (which disables the restriction).

PASS_WARN_AGE (number)

: The number of days warning given before a password expires. A zero means warning is given only upon the day of expiration, a negative value means no warning is given. If not specified, no warning will be provided.

PASS_MAX_DAYS, PASS_MIN_DAYS and PASS_WARN_AGE are only used at the time of account creation. Any changes to these settings won't affect existing accounts.

SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)

When ENCRYPT_METHOD is set to SHA256 or SHA512, this defines the number of SHA rounds used by the encryption algorithm by default (when the number of rounds is not specified on the command line).

With a lot of rounds, it is more difficult to brute forcing the password. But note also that more CPU resources will be needed to authenticate users.

If not specified, the libc will choose the default number of rounds (5000).

The values must be inside the 1000-999,999,999 range.

If only one of the SHA_CRYPT_MIN_ROUNDS or SHA_CRYPT_MAX_ROUNDS values is set, then this value will be used.

If SHA_CRYPT_MIN_ROUNDS > SHA_CRYPT_MAX_ROUNDS, the highest value will be used.

SULOG_FILE (string)

: If defined, all su activity is logged to this file.

SU_NAME (string)

: If defined, the command name to display when running "su -". For example, if this is defined as "su" then a "ps" will display the command is "-su". If not defined, then "ps" would display the name of the shell actually being run, e.g. something like "-sh".

SUB_GID_MIN (number), SUB_GID_MAX (number), SUB_GID_COUNT (number)

: If /etc/subuid exists, the commands useradd and newusers (unless the user already have subordinate group IDs) allocate SUB_GID_COUNT unused group IDs from the range SUB_GID_MIN to SUB_GID_MAX for each new user.
The default values for SUB_GID_MIN, SUB_GID_MAX, SUB_GID_COUNT are respectively 100000, 600100000 and 10000.

SUB_UID_MIN (number), SUB_UID_MAX (number), SUB_UID_COUNT (number)

: If /etc/subuid exists, the commands useradd and newusers (unless the user already have subordinate user IDs) allocate SUB_UID_COUNT unused user IDs from the range SUB_UID_MIN to SUB_UID_MAX for each new user.
The default values for SUB_UID_MIN, SUB_UID_MAX, SUB_UID_COUNT are respectively 100000, 600100000 and 10000.

SYS_GID_MAX (number), SYS_GID_MIN (number)

: Range of group IDs used for the creation of system groups by useradd, groupadd, or newusers.
The default value for SYS_GID_MIN (resp. SYS_GID_MAX) is 101 (resp. GID_MIN-1).

SYS_UID_MAX (number), SYS_UID_MIN (number)

: Range of user IDs used for the creation of system users by useradd or newusers.
The default value for SYS_UID_MIN (resp. SYS_UID_MAX) is 101 (resp. UID_MIN-1).

SYSLOG_SG_ENAB (boolean)

: Enable "syslog" logging of sg activity.

SYSLOG_SU_ENAB (boolean)

: Enable "syslog" logging of su activity - in addition to sulog file logging.

TTYGROUP (string), TTYPERM (string)

The terminal permissions: the login tty will be owned by the TTYGROUP group, and the permissions will be set to TTYPERM.

By default, the ownership of the terminal is set to the user's primary group and the permissions are set to 0600.

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

TTYTYPE_FILE (string)

: If defined, file which maps tty line to TERM environment parameter. Each line of the file is in a format something like "vt100 tty01".

UID_MAX (number), UID_MIN (number)

: Range of user IDs used for the creation of regular users by useradd or newusers.
The default value for UID_MIN (resp. UID_MAX) is 1000 (resp. 60000).

UMASK (number)

The file mode creation mask is initialized to this value. If not specified, the mask will be initialized to 022.

useradd and newusers use this mask to set the mode of the home directory they create

It is also used by pam_umask as the default umask value.

USERDEL_CMD (string)

If defined, this command is run when removing a user. It should remove any at/cron/print jobs etc. owned by the user to be removed (passed as the first argument).

The return code of the script is not taken into account.

Here is an example script, which removes the user's cron, at and print jobs:

#! /bin/sh

# Check for the required argument.
if [ $# != 1 ]; then
        echo "Usage: $0 username"
        exit 1
fi

# Remove cron jobs.
crontab -r -u $1

# Remove at jobs.
# Note that it will remove any jobs owned by the same UID,
# even if it was shared by a different username.
AT_SPOOL_DIR=/var/spool/cron/atjobs
find $AT_SPOOL_DIR -name "[^.]*" -type f -user $1 -delete \;

# Remove print jobs.
lprm $1

# All done.
exit 0

USERGROUPS_ENAB (boolean)

: If set to yes, userdel will remove the user's group if it contains no more members, and useradd will create by default a group with the name of the user.

CROSS REFERENCES

The following cross references show which programs in the shadow password suite use which parameters.

chfn

: CHFN_RESTRICT

chgpasswd

: ENCRYPT_METHOD MAX_MEMBERS_PER_GROUP MD5_CRYPT_ENAB SHA_CRYPT_MAX_ROUNDS SHA_CRYPT_MIN_ROUNDS

chpasswd

: SHA_CRYPT_MAX_ROUNDS SHA_CRYPT_MIN_ROUNDS

gpasswd

: ENCRYPT_METHOD MAX_MEMBERS_PER_GROUP MD5_CRYPT_ENAB SHA_CRYPT_MAX_ROUNDS SHA_CRYPT_MIN_ROUNDS

groupadd

: GID_MAX GID_MIN MAX_MEMBERS_PER_GROUP SYS_GID_MAX SYS_GID_MIN

groupdel

: MAX_MEMBERS_PER_GROUP

groupmems

: MAX_MEMBERS_PER_GROUP

groupmod

: MAX_MEMBERS_PER_GROUP

grpck

: MAX_MEMBERS_PER_GROUP

grpconv

: MAX_MEMBERS_PER_GROUP

grpunconv

: MAX_MEMBERS_PER_GROUP

: CONSOLE_GROUPS DEFAULT_HOME ERASECHAR FAIL_DELAY FAKE_SHELL HUSHLOGIN_FILE KILLCHAR LOGIN_RETRIES LOGIN_TIMEOUT LOG_OK_LOGINS LOG_UNKFAIL_ENAB TTYGROUP TTYPERM TTYTYPE_FILE USERGROUPS_ENAB

newgrp / sg

: SYSLOG_SG_ENAB

newusers

: ENCRYPT_METHOD GID_MAX GID_MIN MAX_MEMBERS_PER_GROUP MD5_CRYPT_ENAB PASS_MAX_DAYS PASS_MIN_DAYS PASS_WARN_AGE SHA_CRYPT_MAX_ROUNDS SHA_CRYPT_MIN_ROUNDS SUB_GID_COUNT SUB_GID_MAX SUB_GID_MIN SUB_UID_COUNT SUB_UID_MAX SUB_UID_MIN SYS_GID_MAX SYS_GID_MIN SYS_UID_MAX SYS_UID_MIN UID_MAX UID_MIN UMASK

pwck

: PASS_MAX_DAYS PASS_MIN_DAYS PASS_WARN_AGE

pwconv

: PASS_MAX_DAYS PASS_MIN_DAYS PASS_WARN_AGE

: CONSOLE_GROUPS DEFAULT_HOME ENV_PATH ENV_SUPATH SULOG_FILE SU_NAME SYSLOG_SU_ENAB

sulogin

: ENV_HZ

useradd

: CREATE_HOME GID_MAX GID_MIN MAIL_DIR MAX_MEMBERS_PER_GROUP PASS_MAX_DAYS PASS_MIN_DAYS PASS_WARN_AGE SUB_GID_COUNT SUB_GID_MAX SUB_GID_MIN SUB_UID_COUNT SUB_UID_MAX SUB_UID_MIN SYS_GID_MAX SYS_GID_MIN SYS_UID_MAX SYS_UID_MIN UID_MAX UID_MIN UMASK

userdel

: MAIL_DIR MAIL_FILE MAX_MEMBERS_PER_GROUP USERDEL_CMD USERGROUPS_ENAB

usermod

: MAIL_DIR MAIL_FILE MAX_MEMBERS_PER_GROUP

BUGS

Much of the functionality that used to be provided by the shadow password suite is now handled by PAM. Thus, /etc/login.defs is no longer used by passwd(1), or less used by login(1), and su(1). Please refer to the corresponding PAM configuration files instead.

Index

NAME
DESCRIPTION
CROSS REFERENCES
BUGS
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 04:45:55 GMT, September 16, 2022

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[MAN] login

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SEE ALSO

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LOGIN

NAME

SYNOPSIS

DESCRIPTION

GNU details

RETURN VALUE

FILES

ATTRIBUTES

CONFORMING TO

NOTES

SEE ALSO

COLOPHON

Index

LOGIN.DEFS

NAME

DESCRIPTION

CROSS REFERENCES

BUGS

SEE ALSO

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