Process management of linux system

Posted by GooberDLX on Sun, 19 Jan 2020 13:19:44 +0100

Preface

We have an operating system to run user programs. The running of programs needs to transfer processes, so process management is the heart of all operating systems.
In fact, a process is the result of current events in the executing program code.

Process understanding

Process:
A process is a static file, a copy of a running program, and has a lifecycle.
Process status:

state	Definition
R(TASK_RUNNING)	Running, ready
S(TASK_INTERRUPTIBLE)	Wake up sleep state
D(TASK_UNINTERRUPTIBLE)	Non wake up sleep state
T(TASK_STOPPED)	Pause state
Z(EXIT_ZOMBIE)	Dead state

The difference between running and ready state is whether it is taking up the cpu time slice

The difference between ready state and wake-up state is whether it is in the queue where the cpu is running

The difference between wake-up and non wake-up is whether it has the system resources needed for the program to run.

ctrl+z can make the process enter the background pause state, which is generally operated by human.

Dead state means that the process has no parent process to recover its system resources, which will cause system resources waste.

Process view

Process tree

[root@workstation Desktop]# pstree
systemd─┬─ModemManager───2*[{ModemManager}]
  	  ├─NetworkManager───2*[{NetworkManager}]
 	  ├─accounts-daemon───2*[{accounts-daemon}]
  ├─agetty
  ├─atd
  ├─auditd─┬─sedispatch
  │        └─2*[{auditd}]
  ├─avahi-daemon───avahi-daemon
  ├─boltd───2*[{boltd}]
  ├─chronyd
  ├─colord───2*[{colord}]
  ├─crond
  ├─cupsd
  ├─dbus-daemon───{dbus-daemon}
  ├─dnsmasq───dnsmasq
  ├─firewalld───{firewalld}
  ...

Process: is the minimum unit of provisioning.
Thread: the object scheduled by the kernel, with independent program counter, process stack and a set of process registers. For linux, threads are special processes. It is also the smallest unit of process operation.
systemd is the daemons.

ps command (display the process status when the current command is executed)
a display terminal related processes (BSD)
x shows all terminal independent processes (BSD)
u display process status information (BSD) by user
f hierarchical display of process information

[root@workstation Desktop]# ps
    PID TTY          TIME CMD
   2499 pts/0    00:00:00 bash
   3273 pts/0    00:00:00 ps
[root@workstation Desktop]# bash
[root@workstation Desktop]# ps
    PID TTY          TIME CMD
   2499 pts/0    00:00:00 bash
   3288 pts/0    00:00:00 bash
   3326 pts/0    00:00:00 ps
[root@workstation Desktop]# ps f
    PID TTY      STAT   TIME COMMAND
   2499 pts/0    Ss     0:00 bash
   3288 pts/0    S      0:00  \_ bash

o specify view options, pid,comm,nice,pri,pcpu,stat,ppid
-e show all processes (uinx)
-f display full format information (unix)
-The H hierarchy displays information about the process
-o specify view options, pid,comm,nice,%cpu,%mem,nice

[root@workstation Desktop]# ps axo pid,comm,nice,stat | less
    PID COMMAND          NI STAT
      1 systemd           0 Ss
      2 kthreadd          0 S
      3 rcu_gp          -20 I<
      4 rcu_par_gp      -20 I<
      6 kworker/0:0H-kb -20 I<
      8 mm_percpu_wq    -20 I<
      9 ksoftirqd/0       0 S
     10 rcu_sched         0 I
     11 migration/0       - S
     12 watchdog/0        - S
     13 cpuhp/0           0 S
     14 cpuhp/1           0 S
     15 watchdog/1        - S

Sort by a parameter:

[root@workstation Desktop]# PS axo PID, comm,% CPU -- sort =% CPU (positive sequence, reverse sequence plus sign)
    PID COMMAND         %CPU
      1 systemd          0.0
      2 kthreadd         0.0
      3 rcu_gp           0.0
      4 rcu_par_gp       0.0
      6 kworker/0:0H-kb  0.0
      8 mm_percpu_wq     0.0
      9 ksoftirqd/0      0.0
     10 rcu_sched        0.0
     ...

ps command display information

 [root@workstation Desktop]# ps aux|less
 USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
 root         1  0.1  0.7 244444 13744 ?        Ss   00:27   0:03 /usr/lib/systemd/systemd --switched-root --system --deserialize 17
 root         2  0.0  0.0      0     0 ?        S    00:27   0:00 [kthreadd]
 root         3  0.0  0.0      0     0 ?        I<   00:27   0:00 [rcu_gp]
 root         4  0.0  0.0      0     0 ?        I<   00:27   0:00 [rcu_par_gp]
 root         6  0.0  0.0      0     0 ?        I<   00:27   0:00 [kworker/0:0H-kblockd]
 root         8  0.0  0.0      0     0 ?        I<   00:27   0:00 [mm_percpu_wq]
 root         9  0.0  0.0      0     0 ?        S    00:27   0:00 [ksoftirqd/0]
 root        10  0.0  0.0      0     0 ?        R    00:27   0:00 [rcu_sched]
 root        11  0.0  0.0      0     0 ?        S    00:27   0:00 [migration/0]
 root        12  0.0  0.0      0     0 ?        S    00:27   0:00 [watchdog/0]
 root        13  0.0  0.0      0     0 ?        S    00:27   0:00 [cpuhp/0]
 root        14  0.0  0.0      0     0 ?        S    00:27   0:00 [cpuhp/1]
 ...

The fields are explained as follows:

field	explain
USER	User name
PID	Process id
%CPU	cpu usage percentage
%MEM	Memory usage percentage
VSZ	Occupied virtual memory size
RSS	Resident memory set size
TTY	Character terminal
STAT	Process state
START	Running time
TIME	cpu time occupied
COMMAND	Process name

pgrep
Display the specified information process
-u uid displays the specified user process
-U name displays the specified user process
-t tty displays the specified terminal process
-l display process name
-a displays the full format process name
-P pid shows the sub processes of the specified process
For example:

[root@workstation Desktop]# id student
  uid=1000(student) gid=1000(student) groups=1000(student),10(wheel)
[root@workstation Desktop]# pgrep -u 1000
  3831
[root@workstation Desktop]# pgrep -l -u 1000
  3831 bash
[root@workstation Desktop]# pgrep -l -U student
  3831 bash
[root@workstation Desktop]# pgrep -l -t pts/1
  3791 bash
  3830 su
  3831 bash
[root@workstation Desktop]# pgrep -la -t pts/1
  3791 bash
  3830 su - student
  3831 -bash
[root@workstation Desktop]# pgrep -P 1
  621
  656
  799
  811
  863
  864
  868
  869
  871
  872
  875
  ...
  [root@workstation Desktop]# pgrep -aP 1
  621 /usr/lib/systemd/systemd-journald
  656 /usr/lib/systemd/systemd-udevd
  799 /usr/bin/rpcbind -w -f
  811 /sbin/auditd
  863 /usr/lib/systemd/systemd-machined
  864 /usr/sbin/mcelog --ignorenodev --daemon --foreground
  868 avahi-daemon: running [workstation.local]
  869 /usr/libexec/udisks2/udisksd
  871 /sbin/rngd -f
  872 /usr/libexec/rtkit-daemon
  875 /usr/sbin/smartd -n -q never
  ...

Pidof (get PID according to process name)
For example:

[root@workstation Desktop]# watch -n 1 date
[root@workstation Desktop]# pidof watch
  4166
[root@workstation Desktop]# ps aux|grep watch
  root        12  0.0  0.0      0     0 ?        S    00:27   0:00 [watchdog/0]
  root        15  0.0  0.0      0     0 ?        S    00:27   0:00 [watchdog/1]
  root        36  0.0  0.0      0     0 ?        S    00:27   0:00 [watchdogd]
  root      4166  0.0  0.1 223888  2844 pts/0    S+   01:42   0:00 watch -n 1 date
  root      4375  0.0  0.0 221864   972 pts/2    S+   01:42   0:00 grep --color=auto watch

top

  Top - 01:46:39 (current system time) 
  Up 1:19 (current system running time),  
  1 user (how many users of the current system are logging in),  
  Load average: 0.10 (queue waiting in one minute), 0.04 (five minutes), 0.01 (fifteen minutes)
  Tasks: 249 total, 2 running, 247 sleeping, 0 stopped, 0 zombie
  %cpu (s): 4.6 us (user), 1.0 sy (kernel), 0.0 Ni (adjust priority), 94.1 ID (idle), 0.0 wa (wait for I / O time), 0.2 hi (hardware interrupt time), 0.0 Si (software interrupt time), 0.2 st (stolen cpu such as virtual machine)
  MIB MEM: 1829.1 total, 211.9 free, 1003.3 used, 613.9 buff / cache
  MIB swap: 0.0 total, 0.0 free, 0.0 used. 640.1 available mem 
  PID (process number)
  USER (USER)
  PR (priority)
  NI (nice value represented by priority)
  VIRT (vsz virtual memory)
  RES (resident memory address)
  SHR (shared resources)
  S (status)
  %cpu (cpu usage)
  %MEM (memory usage)
  TIME+ COMMAND (cpu time is the command name)

top internal parameters:

P cpu percentage sort
M memory percentage
T total cpu time
l turn uptime information on / off
t turn task & CPU information on / off
s adjust refresh rate
k terminate process
u view the specified user process

==top command parameters:==

-d specify refresh interval
-b display in batch mode
-n displays the number of batches

Process priority

The sequence of process's possession of resources

Process types by resource usage

Resource usage	Process type
cpu intensive	CPU-Bound
I/O intensive	I/O-Bound

Priority range
For Linux, priority is divided into a fixed number (0-139)
1-99 refers to real-time priority. The higher the number is, the higher the priority is. The system does not need to be manually processed for its own use
100-139 is static priority, the smaller the number, the higher the priority

NICE value
NICE value: - 20-19 corresponds to static priority 100-139
Ordinary users can only lower the priority and super users can adjust it at will
Commands about priority
• ps ax –o nice,pid,comm
• nice – n priority program
• reince – n priority program pid
For example:

[root@workstation Desktop]# vim
  
  [1]+  Stopped                 vim
[root@workstation Desktop]# ps -o stat,nice,comm,pid
  STAT  NI COMMAND           PID
  Ss     0 bash             2499
  S      0 bash             3288
  T      0 vim              5343
  R+     0 ps               5350

Raise the nice value and check:

[root@workstation Desktop]# renice -n -10 5343
  5343 (process ID) old priority 0, new priority -10
[root@workstation Desktop]# ps -o stat,nice,comm,pid
  STAT  NI COMMAND           PID
  Ss     0 bash             2499
  S      0 bash             3288
  T<   -10 vim              5343
  R+     0 ps               5373

Lower the nice value and view:

[root@workstation Desktop]# renice -n 10 5343
  5343 (process ID) old priority -10, new priority 10
[root@workstation Desktop]# ps -o stat,nice,comm,pid
  STAT  NI COMMAND           PID
  Ss     0 bash             2499
  S      0 bash             3288
  TN    10 vim              5343
  R+     0 ps               5395

Open vim and put it into the background without occupying the terminal:

[root@workstation Desktop]# vim &
  [2] 5474
[root@workstation Desktop]# ps -o stat,nice,comm,pid
  STAT  NI COMMAND           PID
  Ss     0 bash             2499
  S      0 bash             3288
  TN    10 vim              5343
  T      0 vim              5474
  R+     0 ps               5481
  
  [2]+  Stopped                 vim

Specify priority and put it in the background:

[root@workstation Desktop]# nice -n 5 vim &
  [3] 5511
[root@workstation Desktop]# ps -o stat,nice,comm,pid
  STAT  NI COMMAND           PID
  Ss     0 bash             2499
  S      0 bash             3288
  TN    10 vim              5343
  T      0 vim              5474
  TN     5 vim              5511
  R+     0 ps               5518
  
  [3]+  Stopped                 nice -n 5 vim

Call before and after the process

Related commands:

instructions	Meaning
jobs	View background tasks
ctrl+z	Enter the foreground operation task into the background
bg	Activate background process
fg	Repatriation process
&	Running in the background

For example:

[root@workstation Desktop]# jobs
[1]   Stopped                 vim
[2]-  Stopped                 vim
[3]+  Stopped                 nice -n 5 vim

Turn on graphic editing and put it in the background:

[root@workstation Desktop]# gedit
  ^Z
  [4]+  Stopped                 gedit
[root@workstation Desktop]# jobs
  [1]   Stopped                 vim
  [2]   Stopped                 vim
  [3]-  Stopped                 nice -n 5 vim
  [4]+  Stopped                 gedit

Activate background wake up pause process:

[root@workstation Desktop]# bg 4
  [4]+ gedit &
[root@workstation Desktop]# jobs
  [1]   Stopped                 vim
  [2]-  Stopped                 vim
  [3]+  Stopped                 nice -n 5 vim
  [4]   Running                 gedit &

Activate background non wake up pause process:

[root@workstation Desktop]# bg 1
[1] vim &

[1]+  Stopped                 vim
bg Not available here	
[root@workstation Desktop]# fg 1
vim
[root@workstation Desktop]# jobs
[2]-  Stopped                 vim
[3]+  Stopped                 nice -n 5 vim

signal

Controllable signal type
man 7 signal view all signal information

Controllable signal	Meaning
1	Refresh
2	Interrupt keyboard input
3	Quit keyboard
9	Mandatory termination
15	Normal closure
18	Activation process
19	Forced suspension
20	Normal suspension

Signal command
kill signal pid

[root@workstation Desktop]# gedit &
[1] 9662
[root@workstation Desktop]# kill -9 9662
[1]+  Killed                  gedit

Kill signal process name

[root@workstation Desktop]# gedit &
[1] 9628
[root@workstation Desktop]# killall -9 gedit
[1]+  Killed                  gedit

pkill signal conditions (can help to view)

And pgrep Very similar, for example:
[root@workstation Desktop]# su - student
Last login: Sun Jan 19 01:30:16 EST 2020 on pts/1

Open a new shell:

[root@workstation Desktop]# pkill -u 1000

Original shell:

[student@workstation ~]$ logout

System Daemons

Definition of Daemons
Daemon s are usually called daemons, which are the service processes executed in the background of linux. It is independent of the control terminal, periodically executing certain tasks or waiting to handle certain events. It will not stop with the terminal shutdown until receiving the stop information.

Epilogue

You need to configure the network to do the experiment of the daemons, so you can't do it for the time being.

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