who - who is on the system
who [-muTlHqpdbrtasAR] [file]
who am i
who am I
The who command can list the user's name, terminal line, login time,
elapsed time since input activity occurred on the line, the user's
host name, and the process-ID of the command interpreter (shell) for
each current system user. It examines the /etc/utmp file to obtain
its information. If file is given, that file is examined. Usually,
file is /var/adm/wtmp, which contains a history of all of the logins
since the file was last created.
The who command with the am i or am I option identifies the invoking
Except for the default -s option, the general format for output
name [state] line time activity pid [comment] [exit]
With options, who can list logins, logoffs, reboots, and changes to
the system clock, as well as other processes spawned by the init
-m Output only information about the current
terminal. This option is equivalent to the am i
and am I options described above.
-u Lists only those users who are currently logged
in. name is the user's login name. line is the
name of the line as found in the directory /dev.
The time field indicates when the user logged in.
activity is the number of hours and minutes since
input activity last occurred on that particular
line. A dot (.) indicates that the terminal has
seen activity in the last minute and is therefore
``current''. If more than twenty-four hours have
elapsed or the line has not been used since boot
time, the entry is marked old. This field is
useful when trying to determine whether a person
is working at the terminal or not. The pid is the
process-ID of the user's login process. The
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comment is the comment field associated with this
line as found in /etc/inittab (see inittab(4)).
This can contain information about where the
terminal is located, the telephone number of the
dataset, type of terminal if hard-wired, etc. If
no such information is found, then who prints, as
the comment, the user's host name as it was stored
in the /etc/utmp or named file. Note that the
user's host name is printed instead of comments
from the /etc/inittab file if the -u option is
used in conjunction with the -R option.
-T Same as the -u option, except that the state of
the terminal line is printed. state describes
whether someone else can write to that terminal.
A + appears if the terminal is writable by anyone;
a - appears if it is not. root can write to all
lines having a + or a - in the state field. If a
bad line is encountered, a ? is printed.
(XPG4 only.) Only the following fields are
displayed: name state line time
-l Lists only those lines on which the system is
waiting for someone to login. The name field is
LOGIN in such cases. Other fields are the same as
for user entries except that the state field does
-H Prints column headings above the regular output.
-q A quick who, displaying only the names and the
number of users currently logged in. When this
option is used, all other options are ignored.
-p Lists any other process which is currently active
and has been previously spawned by init. The name
field is the name of the program executed by init
as found in /etc/inittab. The state, line, and
activity fields have no meaning. The comment
field shows the id field of the line from
/etc/inittab that spawned this process. See
-d This option displays all processes that have
expired and have not been respawned by init. The
exit field appears for dead processes and contains
the termination and exit values of the dead
process (as returned by wait() - see wait(2)).
This can be useful in determining why a process
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-b Indicates the time and date of the last reboot.
-r Indicates the current run-level of the init
process. The last three fields contain the
current state of init, the number of times that
state has been previously entered, and the
previous state. These fields are updated each
time init changes to a different run state.
-t Indicates the last change to the system clock (via
the date command) by root. See su(1).
-a Processes /etc/utmp or the named file with all
options turned on.
-s Default. Lists only the name, line, and time
-A When the /var/adm/wtmp file is specified, this
option indicates when the accounting system was
turned on or off using the startup or shutacct
commands (see acctsh(1M)). The name field is ..
The line field is acctg on, acctg off, or a reason
that was given as an option to the shutacct
command. The time is the time that the on/off
-R Displays the user's host name. If the user is
logged in on a tty, who displays the string
returned from gethostname() (see gethostname(2)).
If the user is not logged in on a tty and the host
name stored in the /etc/utmp or named file has not
been truncated when stored (meaning that the
entire host name was stored with no loss of
information), it is displayed as it was stored.
Otherwise, the gethostbyaddr() function is called
with the internet address of the host (see
gethostent(3N)). The host name returned by
gethostbyaddr() is displayed unless it returns an
error, in which case the truncated host name is
(XPG4 only. The -s option can not be used with -d, -a or -T options.
If -u option is used with -T, the idle time is added to the end of the
LANG determines the locale to use for the locale categories when both
LC_ALL and the corresponding environment variable (beginning with LC_)
do not specify a locale. If LANG is not set or is set to the empty
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string, a default of "C" (see lang(5)) is used.
LC_CTYPE determines the locale for interpretation of sequences of
bytes of text data as characters (e.g., single- verses multibyte
characters in arguments and input files).
LC_TIME determines the format and contents of date and time strings.
LC_MESSAGES determines the language in which messages are displayed.
If any internationalization variable contains an invalid setting, who
behaves as if all internationalization variables are set to "C". See
International Code Set Support
Single- and multi-byte character code sets are supported.
Check who is logged in on the system:
Check whether or not you can write to the terminal that another user
and look for a plus (+) after the user ID.
who was developed by AT&T and HP.
date(1), login(1), init(1M), mesg(1), su(1), gethostname(2), wait(2),
gethostent(3N), inittab(4), utmp(4).
who: SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2
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