Add condition related to sysctl value in bash file

I would like to execute something only when sysctl vm.max_map_count value is less than 262144. something like:

if [ vm.max_map_count -lt 262144]
then
  sysctl -w vm.max_map_count = 262144
fi

the question is, how to read the value of vm.max_map_count in bash.

Any ideas how to do that?

Solution 1:

The following command:

sysctl -n vm.max_map_count

prints the value without printing the key name. To use the value as an argument to another command, you need command substitution:

if [ "$(sysctl -n vm.max_map_count)" -lt 262144 ]
then …

Note there's a space before ]. Remember [ is a regular command (like ls or echo), not a part of shell syntax; and ] is just the last argument. The [ command requires its last argument to be ]. I'm mentioning this because in your original code the last argument is 262144], it's syntactically wrong.

Also sysctl -w vm.max_map_count = 262144 will not work. The right syntax is sysctl -w vm.max_map_count=262144.