V4/man/man1/who.1

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.th WHO I 3/15/72
.sh NAME
who  \*-  who is on the system
.sh SYNOPSIS
.bd who
[ who-file ]
.sh DESCRIPTION
.it Who,
without an argument,
lists the name, typewriter channel, and login time
for each current UNIX user.
.s3
Without an argument,
.it who
examines the /tmp/utmp
file to obtain its information.
If a file is given, that file is examined.
Typically the given file will be /tmp/wtmp,
which contains a record of all the logins since it
was created.
Then
.it who
will list
logins, logouts, and crashes since the creation of
the wtmp file.
.s3
Each login is listed with user name,
typewriter name (with `/dev/'
suppressed),
and date and time.
When an argument is given, logouts produce a similar line without a user name.
Reboots produce a line with `x' in the place of the device name,
and a fossil time indicative of when the system went down.
.sh FILES
/tmp/utmp
.sh "SEE ALSO"
login(I), init(VII)
.sh BUGS