You are using Centos 5 which is deprecated so nothing in yum will work until you follow this post to use the vault:
http://realtechtalk.com/Centos_59_Working_Vault_Repo_file-1921-articles
yum update
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* epel: fedora-archive.ip-connect.vn.ua
Traceback........
I found the cause of this issue was from all the diskspace being used but clearing it was not enough. Iguess the tables became inconsistent when space ran out and myisamchk is what fixed the rest.
service mysqld restart
ERROR! MySQL manager or server PID file could not be found!
....................................................................................... ERROR! Manager of pid-file quit without updating file.
se........
Loaded plugins: fastestmirror
rpmdb: mmap: No such device
error: db4 error(19) from dbenv->open: No such device
error: cannot open Packages index using db3 - No such device (19)
error: cannot open Packages database in /var/lib/rpm
Traceback (most recent call last):
File "/usr/bin/yum", line 29, in ?
yummain.user_main(sys.argv[1:], exit_code=True)
File "/usr/share/yum-cli/yummain.py&qu........