[Crash-utility] Unable to change the content of memory using crash on a live system

I use crash 4.0-3.9 on a live 2.6.9-55 kernel on i386/i686 as root. crash> ls -l /dev/crash crw------- 1 root root 10, 61 Mar 5 21:57 /dev/crash crash> ls -l /dev/mem crw-r----- 1 root kmem 1, 1 Mar 5 16:49 /dev/mem crash> q [root@linux17081 ~]# ls -l /dev/crash /dev/mem ls: /dev/crash: No such file or directory crw-r----- 1 root kmem 1, 1 Mar 5 16:49 /dev/mem [root@linux17081 ~]# id uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel) So, the /dev/crash file has write permission for me. The I am attempting to change the content of some memory. crash> struct request_queue 0xf7b933f8 struct request_queue { queue_head = { <SNIP> ... } crash> struct -o request_queue | grep in_flight [476] unsigned int in_flight; crash> eval 0xf7b933f8 + 476 hexadecimal: f7b935d4 decimal: 4156110292 (-138857004) octal: 36756232724 binary: 11110111101110010011010111010100 crash> rd f7b935d4 f7b935d4: fffffff1 .... crash> wr f7b935d4 0 wr: cannot write to /dev/crash! I get the error above even if I change the ownership of /dev/kmem to root:root crash> ls -l /dev/mem crw-r----- 1 root root 1, 1 Mar 5 16:49 /dev/mem Am I doing something wrong? How do I change the content of memory on a live system using crash? Dheeraj