Linux operation and maintenance basic process management and environment composition analysis

1. Basic overview of the process
2. Components of a process
3. Process environment
4. Process Status
5. Process Priority
6. Process management commands
7.vmstat
8. Background job running

1. Basic overview of the process

A process is a running instance of an executable program that has been started.

The directories named with numbers under the /proc directory each represent a process and store the attribute information of the process.

The PID of each process is unique. Even if the process exits, other processes will not occupy its PID

2. Components of a process

The address space of allocated memory
Security attributes, including ownership credentials and privileges
One or more threads of execution of program code
Process Status

3. Process environment

Local and global variables
Current scheduling context
Allocated system resources, such as file descriptors and network ports

4. Process Status

Logo	Kernel-defined state names and descriptions
R	TASK_RUNNING: The process is executing on the CPU, or is waiting to run. When in the Running (or Runnable) state, a process may be executing a user routine or a kernel routine (system call), or it may be queued and ready to
S	TASK_INTERRUPTIBLE: The process is sleeping and waiting for a condition: hardware request, system resource access, or signal. When an event or signal satisfies this condition, the process will return to running.
D	TASK_UNINTERRUPTIBLE: This process is also sleeping, but unlike the S state, it will not respond to delivered signals. Use only under specific conditions where process interruption could result in unexpected device states
K	TASK_KILLABLE: The process is in a sleeping state, which is the same as the uninterruptible D state, but modified to allow the waiting task to be interrupted (completely exit) by responding to a signal. Utilities usually display interruptible processes as being in the D state.
T	TASK_STOPPED: The process has been stopped (paused), usually by a signal from the user or another process. The process can be returned to the running state by another signal and continue execution (recovery)
T	TASK_TRACED: The process being debugged will also be temporarily stopped and share the same T status flag
Z	EXIT_ZOMBIE: The child process signals the parent process when it exits. All resources except the process identity (PID) are released
X	EXIT_DEAD: When the parent process cleans up (acquires) the remaining child process structures, the process is now cleanly released. This status is never seen in process listing utilities.
<	High priority process
N	Low priority process
+	Processes in the foreground process group
l	Multithreaded Process
s	Session process head process

5. Process Priority

<0-139>: The smaller the number, the higher the priority!
<0-99>: real-time priority, kernel adjustment
<100-139>: static priority, user controllable

6. Process management commands

The ps command is used to list the current processes. Can display detailed process information

[root@localhost ~]# ps -e
    PID TTY TIME CMD
      1 ? 00:00:02 systemd
      2 ? 00:00:00 kthreadd

[root@localhost ~]# ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.6 179032 13504 ? Ss Nov03 0:02 /usr/lib/syst
root 2 0.0 0.0 0 0 ? S Nov03 0:00 [kthreadd]
root 3 0.0 0.0 0 0 ? I< Nov03 0:00 [rcu_gp]
root 4 0.0 0.0 0 0 ? I< Nov03 0:00 [rcu_par_gp]
root 6 0.0 0.0 0 0 ? I< Nov03 0:00 [kworker/0:0H
root 8 0.0 0.0 0 0 ? I< Nov03 0:00 [mm_percpu_wq
root 9 0.0 0.0 0 0 ? S Nov03 0:00 [ksoftirqd/0]
root 10 0.0 0.0 0 0 ? R Nov03 0:00 [rcu_sched]
root 11 0.0 0.0 0 0 ? S Nov03 0:00 [migration/0]
root 12 0.0 0.0 0 0 ? S Nov03 0:00 [watchdog/0]
root 13 0.0 0.0 0 0 ? S Nov03 0:00 [cpuhp/0]
root 15 0.0 0.0 0 0 ? S Nov03 0:00 [kdevtmpfs]
root 16 0.0 0.0 0 0 ? I< Nov03 0:00 [netns]
root 17 0.0 0.0 0 0 ? S Nov03 0:00 [kauditd]
root 18 0.0 0.0 0 0 ? S Nov03 0:00 [khungtaskd]
root 19 0.0 0.0 0 0 ? S Nov03 0:00 [oom_reaper]
root 20 0.0 0.0 0 0 ? I< Nov03 0:00 [writeback]
root 21 0.0 0.0 0 0 ? S Nov03 0:00 [kcompactd0]
root 22 0.0 0.0 0 0 ? SN Nov03 0:00 [ksmd]
root 23 0.0 0.0 0 0 ? SN Nov03 0:00 [khugepaged]
root 24 0.0 0.0 0 0 ? I< Nov03 0:00 [crypto]
root 25 0.0 0.0 0 0 ? I< Nov03 0:00 [kintegrityd]
root 26 0.0 0.0 0 0 ? I< Nov03 0:00 [kblockd]
root 27 0.0 0.0 0 0 ? I< Nov03 0:00 [tpm_dev_wq]
root 28 0.0 0.0 0 0 ? I< Nov03 0:00 [md]
root 29 0.0 0.0 0 0 ? I< Nov03 0:00 [edac-poller]
root 30 0.0 0.0 0 0 ? S Nov03 0:00 [watchdogd]
root 47 0.0 0.0 0 0 ? S Nov03 0:00 [kswapd0]
root 140 0.0 0.0 0 0 ? I< Nov03 0:00 [kthrotld]
root 141 0.0 0.0 0 0 ? S Nov03 0:00 [irq/24-pcieh
root 142 0.0 0.0 0 0 ? S Nov03 0:00 [irq/25-pcieh
root 143 0.0 0.0 0 0 ? S Nov03 0:00 [irq/26-pcieh
root 144 0.0 0.0 0 0 ? S Nov03 0:00 [irq/27-pcieh
root 145 0.0 0.0 0 0 ? S Nov03

[root@localhost ~]# ps -ef
UID PID PPID C STIME TTY TIME CMD
root 1 0 0 Nov03 ? 00:00:02 /usr/lib/systemd/systemd --s
root 2 0 0 Nov03 ? 00:00:00 [kthreadd]
root 3 2 0 Nov03 ? 00:00:00 [rcu_gp]
root 4 2 0 Nov03 ? 00:00:00 [rcu_par_gp]
root 6 2 0 Nov03 ? 00:00:00 [kworker/0:0H-k

7.vmstat

Virtual memory status view command

vmstat 1000 // indicates that the data is refreshed every 1000 seconds
vmstat 1000 5 //Refresh every 1000 seconds and exit after refreshing 5 times

[root@localhost ~]# vmstat 1000
procs:
    r (running) // indicates the length of the queue waiting to run, that is, the number of processes waiting to run b (block) // indicates the length of the blocking queue, that is, the number of processes in an uninterruptible sleep state memory:
    swpd //Total amount of swap memory used free //Total amount of free physical memory buffer //Total amount of memory used for buffer cache //Total amount of memory used for cache swap:
    si (swap in) // indicates how many pages are swapped from physical memory into swap, that is, the data rate at which data enters swap (kb/s)
    so (swap out) // indicates how many pages are swapped into physical memory from swap, that is, the data rate at which data leaves swap (kb/s)
io:
    bi (block in) //Indicates how many disk blocks are loaded into memory, that is, the rate at which data is read from the block device to the system (kb/s)
    bo (block out) //Indicates how many disk blocks have been synchronized from memory to the hard disk, that is, the rate at which data is saved to the block device (kb/s)
system:
    in (interrupts) // indicates the number of interrupts, that is, the interrupt rate (kb/s)
    cs (context switch) // indicates the number of context switches, that is, the process switching rate (kb/s)
CPU:
    us // indicates user space sy // indicates kernel space id // indicates idle percentage wa // indicates the percentage of time spent waiting for IO to complete st // indicates steal, the time stolen by virtualization technology (such as running a virtual machine)

8. Background job running

// Adding an & symbol after the command will generate a background job [root@localhost ~]# sleep 1000 &
[1] 1400
//The jobs command is used to display all current background jobs [root@localhost ~]# jobs
[1]+ Running sleep 1000 &
//The fg command is used to transfer background jobs to the foreground [root@localhost ~]# fg
//When there is only one background job, use the fg command directly without any parameters to bring the background job to the foreground. However, when there are multiple jobs, you must follow it with %+job number, which is the number enclosed in [] in the command execution result above.
[root@localhost ~]# jobs
[1]- Running sleep 1000 &
[2]+ Running sleep 500 &
[root@localhost ~]# fg %1
//Use ctrl+z to send the foreground process to the background, and the job will be stopped at this time [root@localhost ~]# fg %1
sleep 1000
^Z
[1]+ Stopped sleep 1000
//Use the bg command + job number to restart the stopped background job [root@localhost ~]# bg %1
[1]+ sleep 1000 &
[root@localhost ~]# jobs
[1]- Running sleep 1000 &
[2]+ Running sleep 500 &
//kill plus the job number can manually kill the specified job [root@localhost ~]# jobs
[1]- Running sleep 1000 &
[2]+ Running sleep 500 &
[root@localhost ~]# kill %1
[1]- Terminated sleep 1000
[root@localhost ~]# jobs
[2]+ Running sleep 500 &
//The result of the jobs command + //The command will be the default operation of the job - //The command will be the second default operation of the job

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