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How Are Linux PIDs Generated?
Following the system's interpretation of each command, a separate process is established to carry out the command. This new process is assigned a distinct process identification number (PID). To keep track of each process's current state, the system uses the PID.
Note − Linux commands are case-sensitive.
Process Table
The process table in Linux is just a data structure in a computer's RAM like it is in almost every other operating system. It contains details about the processes that the OS is currently managing.
This data contains broad details about each procedure.
Process Id
Process Owner
Process Priority
Environment variables for each process
Parent Process
Elapsed Time
Pointers to the executable machine code of a process
Run the following command to display a whole screen (or full window of your terminal) with the current condition of your system and a list of the processes utilizing the majority of its CPU.
$ top
Output
top - 13:29:09 up 2 days, 7:13, 4 users, load average: 0.07, 0.02, 0.00
Tasks: 148 total, 1 running, 147 sleeping, 0 stopped, 0 zomb
Cpu(s): 0.6%us, 0.5%sy, 0.0%ni, 97.3%id, 1.6%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 4051792k total, 4026104k used, 25688k free, 359168k buffers
Swap: 4096492k total, 24296k used, 4072196k free, 2806484k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
7629 greys 20 0 749m 291m 28m S 1 7.4 16:51.40 firefox
19935 greys 20 0 133m 14m 10m S 0 0.4 2:38.52 smplayer
331 root 20 0 4020 880 592 S 0 0.0 0:00.96 init
2 root 15 -5 0 0 0 S 0 0.0 0:00.00 /bin/sh
3 root RT -5 0 0 0 S 0 0.0 0:00.04 migration/0
5494 root 15 -5 0 0 0 S 0 0.0 0:00.90 khelper/0
13 root RT -5 0 0 0 S 0 0.0 0:00.00 kacpid
6 root RT -5 0 0 0 S 0 0.0 0:00.06 kacpi_notify
686 root 15 -5 0 0 0 S 0 0.0 0:01.32 ata/1
368 root RT -5 0 0 0 S 0 0.0 0:00.00 ata/0
21 root 15 -5 0 0 0 S 0 0.0 0:02.14 events/0
10 root 15 -5 0 0 0 S 0 0.0 0:01.44 events/1
These are the elements which default top output consists.
PID Generation
Every process has a distinct identifier that serves as a representation of it, known as the process ID (pid). The idle process and its pid number are the names of the initial processes that the kernel launches. With the pid number 1, the init process is the first process to launch after booting.
A system's limit can be determined by consulting the /proc/sys/kernel/pid max file.
$ cat /proc/sys/kernel/pid_max
Output
420314
Then, we determined the system's highest PID. The following step was to start four readlink processes, each of which checks the new PID that was given to it.
largest=0
for pid in /proc/[0-9]*; do
pid="${pid##*/}" # Extract PID
[ "$pid" -gt "$largest" ] && largest="$pid" # -gt means "greater than"
done
printf "Largest PID is %d
" "$largest"
for _ in $(seq 4); do
printf "New process PID %d
" "$(readlink /proc/self)"
done
Output
Largest PID is 12648 New process PID 12650 New process PID 12651 New process PID 12652 New process PID 12653
Due to the seq command's inherent ability to initiate an additional process, we can see that there is a 1 PID delay between checking the highest PID and reporting the new PIDs.
Using ps command
To view the PIDs of running processes using the ps command, you can execute the following command in a terminal.
$ ps aux
Output
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND webmast+ 1 0.0 0.0 1136 0 ? Ss 16:23 0:00 /sbin/docker- webmast+ 7 10.1 0.1 1012 233528 ? Rl 16:23 24:52 GROUND webmast+ 15430 0.0 0.0 2888 908 ? S 16:35 0:00 /bin/sh -c py webmast+ 15431 0.0 0.0 13788 20436 ? Sl 16:35 0:02 python3 main. webmast+ 91894 0.0 0.0 1028 22836 ? S 17:20 0:00 gnuplot webmast+ 91907 0.0 0.0 2888 948 ? S 17:20 0:00 /bin/sh -c oc webmast+ 91908 0.0 0.0 4316732 45844 ? Sl 17:20 0:01 /usr/bin/octa
This command displays a list of processes along with their corresponding PIDs, user information, CPU and memory usage, and other details.
Using pgrep command
When you run the pgrep command with a specific search pattern, it scans the running processes and matches them against the provided criteria. It then returns the PIDs of the processes that meet the search criteria.
Here is an example of using the pgrep command to find processes with a specific name −
$ pgrep <process_name>
Replace <process_name> with the name of the process you want to find. The command will return a list of matching process IDs (PIDs).
For instance, if you want to find the PIDs of processes named "python3", you would run −
Input
$ pgrep python3
Output
15431 173607 189388
The output would be a list of the PIDs of processes with the name "python3".
Conclusion
In this article, we learned about Linux process IDs, what is a process table, including how PIDs are generated. PIDs are essential for managing processes in Linux. The kernel generates a unique PID for each process using a counter and a base PID value. Understanding how PIDs are generated is important for system administrators and developers who need to manage and interact with processes in Linux.
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