unable to do on yum

Im trying to do yum update and yum repolist but no out put showing below error.

please look into below and suggest me soultion.

]# yum repolist
Loaded plugins: rhnplugin, security
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", line 309, in user_main
errcode = main(args)
File "/usr/share/yum-cli/yummain.py", line 166, in main
base.doLock()
File "/usr/lib/python2.4/site-packages/yum/init.py", line 1135, in doLock
while not self._lock(lockfile, mypid, 0644):
File "/usr/lib/python2.4/site-packages/yum/init.py", line 1188, in _lock
if not msg.errno == errno.EEXIST: raise msg
OSError: [Errno 28] No space left on device: '/var/run/yum.pid'