groupdel command is used to delete all entries related to a group in the system. The named group must exist. Syntax: groupdel [options] GROUP
groupmod command in linux is used to modify the information related to any existing group. Syntax groupmod [options] GROUP
groupadd command in linux is used to create a new group. groupadd [Options] group. The list of existing groups in the system is available in /etc/group file
usermod command in linux is used to modify an existing user’s account information. Only the super user can use this command.
userdel command in linux is used to delete an existing user and related files. Only the super user can use this command.
useradd command is used to add a new user in the system. In other words it is used to create a new login account for a different user. useradd command can be used only by the root user.
to set or print the system time and date. date [OPTION]… [+FORMAT]. $date. Output: Tue Aug 27 09:54:25 DST 2019. Explanation : the date command prints the current date and time of the system in a fixed format string as above. The format string is Abbreviated_week_day abbreviated_month day_of_the_month time(hh:mm:ss) time_zone YYYY(year).
Zombie process is a process which has terminated but its entry still exists in the process table until the parent terminates normally or calls wait()
If you are a programmer, you create a program by writing a code and when you run that program it becomes a process. It is very important to have a clear difference between a program and a process because one program can produce many running processes that are just different versions of a single program.