The previous post helped us to understand about Process Overview. This post I will show you about the way processes managed in Unix System.
1. What are Process Identifiers?
Process Identifiers are the unique non-negative integer numbers, used to guarantee uniqueness of the process.
Now check the processes running on your BBB, by using ps command command:
debian@beaglebone:~$ ps -aux
Then you can see PID (Process Identifier) of each process:
debian@beaglebone:~$ ps -aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 1.0 1.0 25540 5096 ? Ss 01:55 0:03 /sbin/init root 2 0.0 0.0 0 0 ? S 01:55 0:00 [kthreadd] root 3 0.0 0.0 0 0 ? I 01:55 0:00 [kworker/0:0] root 4 0.0 0.0 0 0 ? I< 01:55 0:00 [kworker/0:0H] root 6 0.0 0.0 0 0 ? I< 01:55 0:00 [mm_percpu_wq] ... debian 2158 0.0 0.5 27184 2720 ? S 01:56 0:00 (sd-pam) debian 2162 0.1 0.7 5456 3532 ttyS0 S 01:56 0:00 -bash debian 2182 0.0 0.4 6728 2376 ttyS0 R+ 02:00 0:00 ps -aux
There are some special processes:
- PID 0: scheduler process, often known as the swapper. No program on disk corresponds to this process, which is part of the kernel and is known as system process.
- PID 1: the init process and is invoked by the kernel at the end of the bootstrap procedure.
- PID 2: the kthreadd is the kernel thread daemon. All kthreads are forked off this thread.
By using Linux provided function, we can check the PID of running process by using function list:
| Function | Result |
| pid_t getpid(void); | process ID of calling process |
| pid_t getppid(void); | parent process ID of calling process |
| uid_t getuid(void); | real user ID of calling process |
| uid_t geteuid(void); | effective user ID of calling process |
| gid_t getgid(void); | real group ID of calling process |
| gid_t getegid(void); | effective group ID of calling process |
2. Get PID example with BBB
Now let’s build a program and run on BBB, then check all its PID information.
First, open your Linux host machine and create file name 01_PID_checking.c:
#include <unistd.h> /* Header for pid_t type and check PID functions */
#include <stdio.h> /* For printf function */
int main(void)
{
printf("Process ID of calling process is: %d\n", (pid_t) getpid());
printf("Parent process ID of calling process is: %d\n", (pid_t) getppid());
printf("Real user ID of calling process is: %d\n", (pid_t) getuid());
printf("Effective user ID of calling process is: %d\n", (pid_t) geteuid());
printf("Real group ID of calling process is: %d\n", (pid_t) getgid());
printf("Effective group ID of calling process is: %d\n", (pid_t) getegid());
return 0;
}
Build the program using cross compile method I showed you:
arm-linux-gnueabihf-gcc -o 01_PID_checking 01_PID_checking.c
Copy output file from Host machine to your BBB using scp:
sudo scp 01_PID_checking debian@192.168.1.10:/home/debian
Open Teraterm and set 2 connection through SSH, one to run application, the other one for result checking
On BBB, first run your program. This time, your process is created:
debian@beaglebone:~$ ./01_PID_checking Process ID of calling process is: 2349 Parent process ID of calling process is: 2326 Real user ID of calling process is: 1000 Effective user ID of calling process is: 1000 Real group ID of calling process is: 1000 Effective group ID of calling process is: 1000
Then check the result by ps -aux command. You will see your program running
debian@beaglebone:~$ ps -aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 1.0 25540 5096 ? Ss 09:08 0:05 /sbin/init ... debian 2158 0.0 0.5 27184 2720 ? S 09:09 0:00 (sd-pam) debian 2162 0.0 0.7 5456 3532 ttyS0 S+ 09:09 0:00 -bash root 2199 0.0 0.0 0 0 ? I 10:11 0:00 [kworker/0:2] root 2308 0.0 0.0 0 0 ? I 10:19 0:00 [kworker/0:0] root 2311 0.0 0.0 0 0 ? I 10:24 0:00 [kworker/0:1] root 2321 0.3 0.9 9908 4800 ? Ss 10:25 0:00 sshd: debian [priv] debian 2325 0.0 0.7 9908 3724 ? S 10:26 0:00 sshd: debian@pts/0 debian 2326 0.6 0.7 5572 3644 pts/0 Ss 10:26 0:00 -bash root 2335 0.8 0.9 9908 4856 ? Ss 10:26 0:00 sshd: debian [priv] debian 2339 0.3 0.7 9908 3740 ? S 10:26 0:00 sshd: debian@pts/1 debian 2340 1.9 0.7 5572 3644 pts/1 Ss 10:26 0:00 -bash debian 2349 106 0.1 1352 868 pts/0 R+ 10:26 0:05 ./01_PID_checking debian 2350 0.0 0.4 6728 2380 pts/1 R+ 10:26 0:00 ps -aux
Let’s check these number:
- Process ID is 2349, as same as C program and ps command
- Parent PID is 2362, which is process of bash program, reason we call ./01_PID_checking and bash is the default program to run it.
- User ID and Group ID is 1000. Reason is Linux starts creating normal users from UID 1000. Root user will have UID 0. You can check it by yourself by:
debian@beaglebone:~$ sudo su [sudo] password for debian: root@beaglebone:/home/debian# ./01_PID_checking Process ID of calling process is: 2359 Parent process ID of calling process is: 2358 Real user ID of calling process is: 0 Effective user ID of calling process is: 0 Real group ID of calling process is: 0 Effective group ID of calling process is: 0
3. Process termination
Now we will terminate running process by using “kill“:
debian@beaglebone:~$ sudo kill -9 2359
This action will “kill” your running process, then ps -aux, your process is stopped.
4. What should we do next?
In this post, we do an example for process life cycle, and how the Process is managed by PID.
The question is what we can do to create and terminate new process by running process. I will show you the answer in next post.
