/* Void Main's man pages */
{ phpMan } else { main(); }
LOGIN(1) Linux Programmer's Manual LOGIN(1)
NAME
login - sign on
SYNOPSIS
login [ name ]
login -p
login -h hostname
login -f name
DESCRIPTION
login is used when signing onto a system.
If an argument is not given, login prompts for the username.
If the user is not root, and if /etc/nologin exists, the contents of this file are printed to the screen, and the login
is terminated. This is typically used to prevent logins when the system is being taken down.
If special access restrictions are specified for the user in /etc/usertty, these must be met, or the log in attempt will
be denied and a syslog message will be generated. See the section on "Special Access Restrictions".
If the user is root, then the login must be occurring on a tty listed in /etc/securetty. Failures will be logged with
the syslog facility.
After these conditions have been checked, the password will be requested and checked (if a password is required for this
username). Ten attempts are allowed before login dies, but after the first three, the response starts to get very slow.
Login failures are reported via the syslog facility. This facility is also used to report any successful root logins.
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).
Random administrative things, such as setting the UID and GID of the tty are performed. The TERM environment variable is
preserved, if it exists (other environment variables are preserved if the -p option is used). Then the HOME, PATH,
SHELL, TERM, MAIL, and LOGNAME environment variables are set. 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. Last, if this is not a "quiet"
login, the message of the day is printed and the file with the user's name in /var/spool/mail will be checked, and a mes-
sage printed if it has non-zero length.
The user's shell is then 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
above).
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's necessary to create a proper PAM config files (e.g. /etc/pam.d/login and
/etc/pam.d/remote ).
SPECIAL ACCESS RESTRICTIONS
The file /etc/securetty lists the names of the ttys where root is allowed to log in. One name of a tty device without the
/dev/ prefix must be specified on each line. If the file does not exist, root is allowed to log in on any tty.
On most modern Linux systems PAM (Pluggable Authentication Modules) is used. On systems that do not use PAM, the file
/etc/usertty specifies additional access restrictions for specific users. If this file does not exist, no additional
access restrictions are imposed. The file consists of a sequence of sections. There are three possible section types:
CLASSES, GROUPS and USERS. A CLASSES section defines classes of ttys and hostname patterns, A GROUPS section defines
allowed ttys and hosts on a per group basis, and a USERS section defines allowed ttys and hosts on a per user basis.
Each line in this file in may be no longer than 255 characters. Comments start with # character and extend to the end of
the line.
The CLASSES Section
A CLASSES section begins with the word CLASSES at the start of a line in all upper case. Each following line until the
start of a new section or the end of the file consists of a sequence of words separated by tabs or spaces. Each line
defines a class of ttys and host patterns.
The word at the beginning of a line becomes defined as a collective name for the ttys and host patterns specified at the
rest of the line. This collective name can be used in any subsequent GROUPS or USERS section. No such class name must
occur as part of the definition of a class in order to avoid problems with recursive classes.
An example CLASSES section:
CLASSES
myclass1 tty1 tty2
myclass2 tty3 @.foo.com
This defines the classes myclass1 and myclass2 as the corresponding right hand sides.
The GROUPS Section
A GROUPS section defines allowed ttys and hosts on a per Unix group basis. If a user is a member of a Unix group accord-
ing to /etc/passwd and /etc/group and such a group is mentioned in a GROUPS section in /etc/usertty then the user is
granted access if the group is.
A GROUPS section starts with the word GROUPS in all upper case at the start of a line, and each following line is a
sequence of words separated by spaces or tabs. The first word on a line is the name of the group and the rest of the
words on the line specifies the ttys and hosts where members of that group are allowed access. These specifications may
involve the use of classes defined in previous CLASSES sections.
An example GROUPS section.
GROUPS
sys tty1 @.bar.edu
stud myclass1 tty4
This example specifies that members of group sys may log in on tty1 and from hosts in the bar.edu domain. Users in group
stud may log in from hosts/ttys specified in the class myclass1 or from tty4.
The USERS Section
A USERS section starts with the word USERS in all upper case at the start of a line, and each following line is a
sequence of words separated by spaces or tabs. The first word on a line is a username and that user is allowed to log in
on the ttys and from the hosts mentioned on the rest of the line. These specifications may involve classes defined in
previous CLASSES sections. If no section header is specified at the top of the file, the first section defaults to be a
USERS section.
An example USERS section:
USERS
zacho tty1 @130.225.16.0/255.255.255.0
blue tty3 myclass2
This lets the user zacho login only on tty1 and from hosts with IP addreses in the range 130.225.16.0 - 130.225.16.255,
and user blue is allowed to log in from tty3 and whatever is specified in the class myclass2.
There may be a line in a USERS section starting with a username of *. This is a default rule and it will be applied to
any user not matching any other line.
If both a USERS line and GROUPS line match a user then the user is allowed access from the union of all the ttys/hosts
mentioned in these specifications.
Origins
The tty and host pattern specifications used in the specification of classes, group and user access are called origins.
An origin string may have one of these formats:
o The name of a tty device without the /dev/ prefix, for example tty1 or ttyS0.
o The string @localhost, meaning that the user is allowed to telnet/rlogin from the local host to the same host.
This also allows the user to for example run the command: xterm -e /bin/login.
o A domain name suffix such as @.some.dom, meaning that the user may rlogin/telnet from any host whose domain name
has the suffix .some.dom.
o A range of IPv4 addresses, written @x.x.x.x/y.y.y.y where x.x.x.x is the IP address in the usual dotted quad deci-
mal notation, and y.y.y.y is a bitmask in the same notation specifying which bits in the address to compare with
the IP address of the remote host. For example @130.225.16.0/255.255.254.0 means that the user may rlogin/telnet
from any host whose IP address is in the range 130.225.16.0 - 130.225.17.255.
o An range of IPv6 addresses, written @[n:n:n:n:n:n:n:n]/m is interpreted as a [net]/prefixlen pair. An IPv6 host
address is matched if prefixlen bits of net is equal to the prefixlen bits of the address. For example, the
[net]/prefixlen pattern [3ffe:505:2:1::]/64 matches every address in the range 3ffe:505:2:1:: through
3ffe:505:2:1:ffff:ffff:ffff:ffff.
Any of the above origins may be prefixed by a time specification according to the syntax:
timespec ::= '[' <day-or-hour> [':' <day-or-hour>]* ']'
day ::= 'mon' | 'tue' | 'wed' | 'thu' | 'fri' | 'sat' | 'sun'
hour ::= '0' | '1' | ... | '23'
hourspec ::= <hour> | <hour> '-' <hour>
day-or-hour ::= <day> | <hourspec>
For example, the origin [mon:tue:wed:thu:fri:8-17]tty3 means that log in is allowed on mondays through fridays between
8:00 and 17:59 (5:59 pm) on tty3. This also shows that an hour range a-b includes all moments between a:00 and b:59. A
single hour specification (such as 10) means the time span between 10:00 and 10:59.
Not specifying any time prefix for a tty or host means log in from that origin is allowed any time. If you give a time
prefix be sure to specify both a set of days and one or more hours or hour ranges. A time specification may not include
any white space.
If no default rule is given then users not matching any line /etc/usertty are allowed to log in from anywhere as is stan-
dard behavior.
FILES
/var/run/utmp
/var/log/wtmp
/var/log/lastlog
/var/spool/mail/*
/etc/motd
/etc/passwd
/etc/nologin
/etc/usertty
/etc/pam.d/login
/etc/pam.d/remote
.hushlogin
SEE ALSO
init(8), getty(8), mail(1), passwd(1), passwd(5), environ(7), 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 satisfac-
tory substitute. Indeed, for security reasons, login does a vhangup() system call to remove any possible listening pro-
cesses 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'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 (gladATdaimi.dk) for HP-UX
Ported to Linux 0.12: Peter Orbaek (poeATdaimi.dk)
AVAILABILITY
The login command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-
linux-ng/.
Util-linux 1.6 4 November 1996 LOGIN(1)
