/proc/PID/statからプロセスの起動時刻を知る

gistfile1.pl

use POSIX qw(strftime sysconf _SC_CLK_TCK);
use File::Slurp;
use Time::Piece;
use Time::HiRes qw(time);

my $TIME_OF_BOOT = time_of_boot();
my $CLOCK_TICK   = sysconf(_SC_CLK_TCK);

MAIN: {
    my $pid = shift or die "missing PID";

    my $stat = read_file("/proc/$pid/stat");
    my @stats = split /\s+/, $stat;
    my $start_unix_time = convert_into_start_unix_time($stats[21]);
    printf("%s: since %s (%d)\n",
           $pid,
           localtime($start_unix_time)->datetime,
           $start_unix_time,
          );
}

sub time_of_boot {
    open my $u, '<', '/proc/uptime' or die $!;
    my $buf = <$u>;
    my($seconds_since_boot) = (split /\s+/, $buf);
    close $u;
    return time() - $seconds_since_boot;
}

sub convert_into_start_unix_time {
    my $start_time_jiffies = shift;
    return int( $TIME_OF_BOOT + ($start_time_jiffies / $CLOCK_TICK) );
}