If you are trying to use a command, fuser, that is used to identify process using lock file or socket file, and having the following error:
-bash: fuser: command not found
that means, your system doesn’t have the psmisc package installed. Usually, killall, fuser type of commands are under this package. CentOS 7 sometimes, do not install the package by default. To install it, run the following:
yum install psmisc -y
Once done, you should be able to use fuser command.