8 Execução de comandos

O Zabbix usa uma funcionalidade em comum para executar parâmetros de usuários, comandos remotos, system.run[] sem a flag "nowait", scripts (alerta, externos e globais) e outros comandos internos.

O comando/script é executado de forma similar nas plataformas UNIX e Windows:

1. Zabbix (um de seus processos) cria uma ponte para comunicação
2. Zabbix configura a pote como a saída para o processo a ser criado
3. Zabbix cria o processo filho (executa o comando/script)
4. Um novo grupo de processos (no Unix) ou um 'job' (no Windows) é criado para os processos filhos
5. O Zabbix lê do 'pipe' até que o 'timeout' seja alcançado ou que ninguém esteja mais gravando nele (Todos os gerenciadores/descritores de arquivo tiverem sido fechados). Observe que o processo filho pode criar mais processos e sair antes de ter saido ou fechado o descritor de arquivo.
6. Se o tempo limite não tiver sido alcançado o Zabbix aguarda até que o processo saia ou que o timeout ocorra
7. Neste ponto nós estamos assumindo que tudo foi executado com sucesso e toda a árvore de processos foi terminada

Todas as aspas duplas e contrabarras no comando serão escapadas com contrabarras e o comando será executado entre aspas duplas.

Leia mais sobre isso nos manuais de parâmetros de usuário, comandos remotos, scripts de alerta.

Execution steps

The command/script is executed similarly on both Unix and Windows platforms:

1. Zabbix (the parent process) creates a pipe for communication
2. Zabbix sets the pipe as the output for the to-be-created child process
3. Zabbix creates the child process (runs the command/script)
4. A new process group (in Unix) or a job (in Windows) is created for the child process
5. 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.
6. If the timeout has not been reached, Zabbix waits until the initial child process exits or timeout occurs
7. If the initial child process exited and the timeout has not been reached, Zabbix checks exit code of the initial child process and compares it to 0 (non-zero value is considered as execution failure, only for custom alert scripts, remote commands and user scripts executed on Zabbix server and Zabbix proxy)
8. 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

All double quotes and backslashes in the command are escaped with backslashes and the command is enclosed in double quotes.

Exit code checking

Exit code are checked with the following conditions:

• Only for custom alert scripts, remote commands and user scripts executed on Zabbix server and Zabbix proxy.
• Any exit code that is different from 0 is considered as execution failure.
• Contents of standard error and standard output for failed executions are collected and available in frontend (where execution result is displayed).
• Additional log entry is created for remote commands on Zabbix server to save script execution output and can be enabled using LogRemoteCommands agent parameter.

Possible frontend messages and log entries for failed commands/scripts:

• Contents of standard error and standard output for failed executions (if any).
• "Process exited with code: N." (for empty output, and exit code not equal to 0).
• "Process killed by signal: N." (for process terminated by a signal, on Linux only).
• "Process terminated unexpectedly." (for process terminated for unknown reasons).

Read more about:

• External checks
• User parameters
• system.run items
• Custom alert scripts
• Remote commands
• Global scripts