Sometimes when you browse solution to some issue, you might have seen “make sure your kernel supports —- option i.e. during its build, this option is specified and enabled ?”
So the answer lies in this article.
Today we will see a very useful tip to identify whether our kernel is built with some specific option or not.
1. First check out the current kernel through which our system is booted with.
[root@ngelinux cgroup]# uname -a Linux ngelinux 3.10.0-957.el7.x86_64 #1 SMP Thu Nov 8 23:39:32 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux [root@ngelinux cgroup]#
Hence our system is up with kernel version 3.10.0-957.
2. Check Kernel config file for options.
To know with which option this kernel is created, check out the config file kept inside /boot and grep the option you want to look for.
[root@ngelinux cgroup]# cat /boot/config-3.10.0-957.el7.x86_64 | grep -i cgroup CONFIG_CGROUPS=y # CONFIG_CGROUP_DEBUG is not set CONFIG_CGROUP_FREEZER=y CONFIG_CGROUP_PIDS=y CONFIG_CGROUP_DEVICE=y CONFIG_CGROUP_CPUACCT=y CONFIG_CGROUP_HUGETLB=y CONFIG_CGROUP_PERF=y CONFIG_CGROUP_SCHED=y CONFIG_BLK_CGROUP=y # CONFIG_DEBUG_BLK_CGROUP is not set CONFIG_NETFILTER_XT_MATCH_CGROUP=m CONFIG_NET_CLS_CGROUP=y CONFIG_NETPRIO_CGROUP=y [root@ngelinux cgroup]#
We can see above most of the cgroup config is set and few of the options are not set.
3. An example: checking ikconfig option
[root@ngelinux cgroup]# cat /boot/config-3.10.0-957.el7.x86_64 | grep -i ikconfig # CONFIG_IKCONFIG is not set
If our kernel was built with IKCONFIG_PROC option set, we can check out the configuration from /proc/config.gz file as it is built with IKCONFIG enabled, and then we can extract it from kernel image by using extract-ikconfig script.
4. Verifying if our kernel supports CGROUPs.
To use crgroups and its features, our kernel must built with option CONFIG_CGROUP.
We can see above that our kernel is built with this option enabled and hence CGROUPs are supported.
[root@ngelinux cgroup]# cat /boot/config-3.10.0-957.el7.x86_64 | grep -i cgroup CONFIG_CGROUPS=y
- Each CGROUP v1 controller has an associated configuration option that must be set in order to use that controller.
Each controller must be mounted against a cgroup filesystem.
Such mounts go under tmpfs filesystem mounted at /sys/fs/cgroup.
- For example:- We can mount cpu controller as follows:
# mount -t cgroup -o cpu none /sys/fs/cgroup/cpu