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

[Dheeraj Sangamkar]

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 at 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 at 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
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