Basic Exec

Today, we are trying 'exec'.  There are few variants of exec.  To start with we will concentrate on one variant 'execl'.

1. After this function call, current process will be replaced with exec and current process will no longer exist
2. First arg: full path of command to execute. Second arg: Name of the program. Third Arg and so on: Optional. Arguments passed to command. End of arguments specified by 'NULL'.
3. Rest of the program after exec will be ignored as the current program no longer exists.

1 2 3 4 5 6 7 8 9 10

#include <stdio.h> #include <unistd.h> int main() { printf("PID of the process %d\n",getpid()); printf("Sleep using exec\n"); execl("/bin/sleep","sleep","5",NULL); printf("lines after exec\n"); }

Execute the program, and immediately in another terminal issue 'ps -a'

# ./a.out
PID of the process 4628
Sleep using exec

# ps -a
  PID TTY          TIME CMD
 1668 tty1     00:01:34 Xorg
 1674 tty1     00:00:00 gnome-session-b
 1767 tty1     00:00:00 gnome-keyring-d
 1775 tty1     00:01:50 gnome-shell
 1893 tty1     00:00:03 gnome-settings-
 1919 tty1     00:00:00 zeitgeist-datah
 1924 tty1     00:00:04 nautilus
 1926 tty1     00:00:00 tracker-extract
 1935 tty1     00:00:00 tracker-miner-a
 1936 tty1     00:00:00 tracker-miner-f
 1937 tty1     00:00:00 tracker-miner-u
 1960 tty1     00:00:00 gsd-printer
 3639 pts/0    00:11:38 firefox-esr
 4584 tty1     00:00:00 gvim
 4628 pts/1    00:00:00 sleep
 4630 pts/2    00:00:00 ps 

Observations are:

•  process ID of current program 4628 and the process ID of sleep command in 'ps -a' output are the same.  sleep replaced current program
• Line 9 of the current program is not executed.  It is ignored.