How to send a signal to a process in Linux? How to change permissions on a file/directory?

To send a signal to a process in Linux, the kill command is used with the PID and signal type:

kill -SIGTERM <pid>   # Send termination signal
kill -9 <pid>         # Forcefully terminate the process (SIGKILL)

To change permissions on a file or directory, the chmod command is used:

chmod 755 filename    # Set permissions rwxr-xr-x
chmod u+x script.sh   # Add execute permission for the owner

Permissions are set for the owner (u), group (g), and others (o), and can be specified using numeric or symbolic notation.

Example:

chmod 644 file.txt    # rw-r--r--
chmod g+w dir         # Add write permission to the group