This trick wotks on Centos 5/6

dmesg | awk -F ] ‘{“cat /proc/uptime | cut -d \” \” -f 1″ | getline st;a=substr( $1,2, length($1) – 1);print strftime(“%F %H:%M:%S %Z”,systime()-st+a)” -> “$0}’

If you have Fedora and systemd, so:

journalctl -a | less