[Linux] PHP Programmers play Linux series-using supervisor to implement Daemons

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The first problem is that when you deploy Nodejs's blog, I put the command to execute Nodejs in the background, using the Add & and Nohup commands

such as: Nodejs Index.js & or Nohup Nodejs index.js &

& This use is when exiting the terminal session will stop, nohup This command can theoretically be executed in the background, but when there are some exceptions, will still exit.

Basic concepts of processes

A process is the process of executing a program. The Ppid of the Unix system's ancestor kernel process is 0, for example: The PID of the init process is 1,ppid 0; the other processes are forked from the init process, and the process tree is visible using the pstree command.

Test use & Implement a background process, and the background process back to the foreground, the following is to put the process into the background, [1] This is the job number

The background process is re-forwarded to the foreground, and the%1 number is the job number above

FG%1

How to use the Nohup command

The Nohup command, which is a command that causes the process to ignore the Sighup hang (hangup) signal, is tested as follows:

Nohup ping baidu.com > Xx.txt &

The process signals are as follows:

SIGHUP suspend (hangup) SIGINT interrupt, when the user from the keyboard to press the ^C or ^break key when the Sigquit exit, when the user press the QUIT key from the keyboard Sigill illegal instructions SIGTRAP tracking traps (trace trap), Start process, trace Code execution sigiot iot Directive sigemt EMT Instruction SIGFPE floating-point arithmetic overflow SIGKILL kill, terminate process Sigbus bus error one SIGSEGV segment violation (segmentation
   
    violation), the process attempts to access a location other than its virtual address space of the Sigsys system call in the wrong parameter, such as the system call number illegal sigpipe write data to a non-read pipeline sigalrm alarm. This signal is sent when a process wants to receive a signal after a certain time. SIGTERM software termination (software  termination) SIGUSR1 user-defined signal 117 SIGUSR2 user-defined signal 218 SIGCLD a child process dead 19 SIGPWR Power failure
   

　　

Implementing Daemons using Supervisor

The daemon is a process that has been running for a long period of time. Using supervisor, you can implement such a process, which is automatically restarted when it is killed.

#安装supervisoryum Install Supervisor

Configure the configuration file (/etc/supervisord.conf):

Program:nodejsblog here: The back is a name, you can start casually
command= here is the command to execute
User= here is the execution user

[Program:nodejsblog]command=/usr/bin/nodejs/var/www/html/nblog index.js User=root

Open Supervisord-c/etc/supervisord.conf

At this point the Nodejs daemon will also be able to check with the PS command as it is started, and will automatically restart when you kill the process.

For example, I test the deployment of the Nodejs site in this example http://nblog.qingguow.cn

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[Linux] PHP Programmers play Linux series-using supervisor to implement Daemons