proxy# sh /usr/src/linux-2.6.21/scripts/ver_linux 
If some fields are empty or look unusual you may have an old version.
Compare to the current minimal requirements in Documentation/Changes.
 
Linux proxy 2.6.21.6 #1 SMP Mon Jul 30 17:25:54 EEST 2007 x86_64 x86_64 x86_64 GNU/Linux
 
Gnu C                  3.4.6
Gnu make               3.81
binutils               2.16.92
util-linux             2.12r
mount                  2.12r
module-init-tools      3.2.2
e2fsprogs              1.38
xfsprogs               2.8.10
PPP                    2.4.4
Linux C Library        2.3.6
Dynamic linker (ldd)   2.3.6
Procps                 3.2.7
Net-tools              1.60
Kbd                    85:
Sh-utils               5.97
Modules Loaded         sch_tbf ppp_async crc_ccitt ppp_generic slhc xt_multiport ipt_REJECT xt_state xt_limit xt_TCPMSS xt_tcpudp iptable_nat nf_nat nf_conntrack_ipv4 nf_conntrack nfnetlink iptable_filter ip_tables x_tables sch_sfq ip_gre nfsd exportfs lockd sunrpc r8168