Regular users can automate particular jobs to run when they log in, or at certain times, or on certain days. The system administrator can use the same mechanisms to run system processes periodically.
It is possible to automate commands (and hence jobs) to run automatically whenever you log in to UNIX. These commands may also set up your desired environment by setting shell variables that control the environment. Two files are executed by every Bourne or Korn shell user during login:
.profile (in the user’s home directory)
Only the root user can modify /etc/profile because changes in that file affect the logins for all users. For security reasons, ...