V6/usr/man/man5/wtmp.5

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including files from this version of Unix. 
.th WTMP V 2/22/74
.sh NAME
wtmp \*- user login history
.sh DESCRIPTION
This
file records all logins and logouts.
Its format is exactly like utmp (V) except that
a null user name indicates a logout on the associated
typewriter.
Furthermore, the typewriter name `~' indicates that the
system was rebooted at the indicated time;
the adjacent pair of entries with typewriter names
`|' and `}' indicate the system-maintained time
just before and just after a
.it date
command has changed the system's idea of the time.
.s3
.it Wtmp
is maintained by login (I) and init (VIII).
Neither of these programs creates the file,
so if it is removed record-keeping is turned off.
It is summarized by ac (VIII).
.sh FILES
/usr/adm/wtmp
.sh "SEE ALSO"
utmp (V), login (I), init (VIII), ac (VIII), who (I)