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manual:appendix:command_execution [2017/10/10 14:32]
manual:appendix:command_execution [2017/12/14 13:14]
natalja.cernohajeva Numeration edited.
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 +==== 9 Command execution ====
 +Zabbix uses common functionality to execute user parameters, remote commands,[] items without the "​nowait"​ flag, scripts (alert, external and global) and some internal commands. ​
 +The command/​script is executed similarly on both Unix and Windows platforms:
 +  - Zabbix (the parent process) creates a pipe for communication
 +  - Zabbix sets the pipe as the output for the to-be-created child process
 +  - Zabbix creates the child process (runs the command/​script)
 +  - A new process group (in Unix) or a job (in Windows) is created for the child process
 +  - Zabbix reads from the pipe until timeout occurs or no one is writing to the other end (ALL handles/​file descriptors have been closed). Note that the child process can create more processes and exit before they exit or close the handle/file descriptor.
 +  - If the timeout has not been reached, Zabbix waits until the initial child process exits or timeout occurs
 +  - At this point it is assumed that everything is done and the whole process tree (i.e. the process group or the job) is terminated
 +<note important>​Steps 5-7 do not refer to remote commands as they are executed with a "​nowait"​ flag.</​note>​
 +<note important>​Zabbix assumes that a command/​script has done processing when the initial child process has exited AND no other process is still keeping the output handle/file descriptor open. When processing is done, ALL created processes are terminated.</​note>​
 +All double quotes and backslashes in the command are escaped with backslashes and the command is enclosed in double quotes.
 +Read more about [[manual:​config:​items:​userparameters|user parameters]],​ [[manual:​config:​notifications:​action:​operation:​remote_command|remote commands]], [[manual:​config:​notifications:​media:​script|alert scripts]].