When you log in to a Unix system, it tells you when you last logged in. That information is stored in a binary file called lastlog. Each user has their own record; UID 8 is at record 8, UID 239 at record 239, and so on. To find out when a given user last logged in, convert their login name to a number, seek to their record in that file, read, and unpack. Doing so with shell tools is hard, but with the laston program, it''s easy. Here''s an example:
% laston gnat gnat UID 314 at Mon May 25 08:32:52 2003 on ttyp0 from below.perl.com
The program in Example 8-9 is much newer than the tctee program in Example 8-8, but it''s less portable. It uses the Linux binary layout of the lastlog file. You''ll have to change this for other systems.
#!/usr/bin/perl -w
# laston - find out when given user last logged on
use User::pwent;
use IO::Seekable qw(SEEK_SET);
open (LASTLOG, "< :raw", "/var/log/lastlog")
or die "can''t open /var/log/lastlog: $!";
$typedef = "L A12 A16"; # linux fmt; sunos is "L A8 A16"
$sizeof = length(pack($typedef, ( )));
for $user (@ARGV) {
$U = ($user =~ /^\d+$/) ? getpwuid($user) : getpwnam($user);
unless ($U) { warn "no such uid $user\n"; next; }
seek(LASTLOG, $U->uid * $sizeof, SEEK_SET) or die "seek failed: $!";
read(LASTLOG, $buffer, $sizeof) = = $sizeof or next;
($time, $line, $host) = unpack($typedef, $buffer);
printf "%-8s UID %5d %s%s%s\n", $U->name, $U->uid,
$time ? ("at " . localtime($time)) : "never logged in",
$line && " on $line",
$host && " from $host";
}