Sessreg is a simple program for managing utmp/wtmp
entries for xdm sessions.
System V has a better interface to utmp than BSD; it
dynamically allocates entries in the file, instead of writing them at fixed
positions indexed by position in
/etc/ttys.
To manage BSD-style utmp files, sessreg has two strategies. In
conjunction with xdm, the -x option counts the number of lines in
/etc/ttys
and then adds to that the number of the line in the Xservers file which
specifies the display. The display name must be specified as the
"line-name" using the -l option. This sum is used as the "slot-number" in
the utmp file that this entry will be written at. In the more general case,
the -s option specifies the slot-number directly. If for some strange reason
your system uses a file other than
/etc/ttys
to manage init, the -t option can direct
sessreg to look elsewhere for a count of terminal sessions.
Conversely, System V managers will not ever need to use these options (-x,
-s and -t). To make the program easier to document and explain,
sessreg accepts the BSD-specific flags in the System V
environment and ignores them.
BSD and Linux also have a host-name field in the utmp file which doesn't
exist in System V. This option is also ignored by the System V version of
sessreg.