----- Original Message ----- Thanks for diving into this kernel subsystem. Given the emergence of cgroups, this command could ultimately be considered as a new built-in command. However, that being said, it does need some additional work. First, for older kernels that don't have cgroups, there should be a protection mechanism to prevent this from happening: crash> sys | grep RELEASE RELEASE: 2.6.18-146.el5 crash> lscgroup lscgroup: invalid structure member offset: cgroupfs_root_root_list FILE: lscgroup.c LINE: 503 FUNCTION: cgroup_list_cgroups() [/usr/bin/crash] error trace: 4611e1 => 7f3b8f3a19d7 => 7f3b8f3a14e6 => 50b701 50b701: OFFSET_verify+161 4611e1: exec_command+801 lscgroup: invalid structure member offset: cgroupfs_root_root_list FILE: lscgroup.c LINE: 503 FUNCTION: cgroup_list_cgroups() crash> You should check for the existence of a kernel variable or structure definition, and if they don't exist, call command_not_supported(). Secondly, if I am not mistaken, your command only shows "enabled" cgroups? So for example, on this RHEL6 system, the command quietly does nothing: crash> sys | grep RELEASE RELEASE: 2.6.32-15.el6.x86_64 crash> lscgroup crash> Is that the case? I wonder if you should also show cgroups that are not enabled, i.e., like /proc/cgroups does? Or at a minimum, it should show display something like "(no cgroups enabled)" instead of just showing nothing at all. Thirdly, your help page shows a "-h" option, which is unnecessary: crash> help lscgroup NAME lscgroup - list all cgroups SYNOPSIS lscgroup lscgroup [<controllers>:<path>] [...][-h] ... because it doesn't do anything other than show the SYNOPSIS line from the "help lscgroup" output: crash> lscgroup -h Usage: lscgroup lscgroup [<controllers>:<path>] [...][-h] Enter "help lscgroup" for details. crash> And you should change the third line in help_lscgroup[] from: char *help_lscgroup[] = { "lscgroup", "list all cgroups", "lscgroup [<controllers>:<path>] [...][-h]", to: "[<controllers>:<path>] [...][-h]", so that "lscgroup" is not printed twice in the "help lscgroup" and the "Usage:" output. And lastly, and most importantly, is what the command does *not* show. Consider that most crash commands that delve into kernel subsystems typically show information intermingled with key data structure addresses. So if there is a bug associated with a kernel subsystem, the data structure addresses displayed by a crash command can be used as a starting point for debugging purposes. So for example, if there was a bug associated with cgroups, your command's output only shows the name strings, but there's nothing else to "work with" for debugging. Wouldn't it be more helpful to at least display the cgroup and/or the cgroupfs_root addresses? Then there would be useful data structure addresses to start with. Thanks, Dave