いろいろなバージョンを確認するコマンドをまとめておきます。
CentOS
$ cat /etc/redhat-release
CentOS release 5.5 (Final)
Fedora 8
$ cat /etc/fedora-release
Fedora release 8 (Werewolf)
/etc/system-releaseでもOKです。
$ cat /etc/system-release
Fedora release 8 (Werewolf)
/etc/system-releaseは/etc/fedora-releaseへのシンボリックリンクになっています。
$ls -la /etc/system-release
lrwxrwxrwx 1 root root 14 Nov 24 2009 /etc/system-release -> fedora-release
Amazon Linux
$ cat /etc/system-release
Amazon Linux AMI release 2010.11.1 (beta)
FreeBSD
$ uname -a
FreeBSD tetsuyai.com 7.2-RELEASE FreeBSD 7.2-RELEASE #0: Fri May 1 08:49:13 UTC 2009 root@walker.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC i386
Apache
$ /usr/sbin/httpd -v
Server version: Apache/2.2.3
Server built: Aug 30 2010 12:28:40
Nginx
$ /usr/sbin/nginx -v
nginx version: nginx/0.6.33
Phusion Passenger
$ passenger-config --version
2.2.15
MySQL
mysql> select version();
+------------+
| version() |
+------------+
| 5.0.77-log |
+------------+
1 row in set (0.03 sec)
Ruby
$ ruby --version
ruby 1.8.7 (2010-08-16 patchlevel 302) [x86_64-linux]
RubyGems
$ gem --version
1.3.7
Rails
$ rails --version
Rails 3.0.0