Linux KILL command gives you killing opportunities to use SIGNALs. In this post we’re going to Pause (or suspend) and Start an ongoing Linux process.<\/p>\n\n\n\n
Problem: The requirement here is to pause a process for certain time and run it only during off hours. The process itself doesn’t have this option and also we cannot stop it in-between, as it will start from the scratch again.<\/p>\n\n\n\n
Solution: To resolve this we can think of sending out signals to the process to hint it to Pause or Progress.<\/p>\n\n\n\n
\nA signal is an asynchronous notification sent to a process or to a specific thread within the same process in order to notify it of an event that occurred. When a signal is sent, the operating system interrupts the target process’ normal flow of execution to deliver the signal.<\/p>\n<\/blockquote>\n\n\n\n\n\n\n\n
For a command run on terminal we may use ctrl+z to suspend the process. This internally sends the SIGTSTP signal to the foreground process. Which will basically pause the execution of the command and return control to the terminal.<\/p>\n\n\n\n
We can later use bg – to send the execution in background or fg – to bring the process in foreground for proceeding the execution.<\/p>\n\n\n\n
Though here we don’t have terminal access and we need to work on a different process using script. We will use KILL command with two signals SIGTSTP & SIGCONT to achieve the goal. All we need is the PID of the target process.<\/p>\n\n\n\n
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- SIGTSTP, by default, causes the process to suspend execution. Our Pause.<\/li>\n\n\n\n
- SIGCONT will continue executing the process, if stopped. That’s our Start.<\/li>\n<\/ul>\n\n\n\n
The Script to Pause\/Start Linux Process:<\/h2>\n\n\n\n
[root@nitty-witty sigscripts]# cat .\/signal.sh\nstop() {\nkill -TSTP $1\n}\n\nstart() {\nkill -SIGCONT $1\n}\n\nusage() {\necho \"$1 [stop|start] process_id\"\n}\n\nif [ \"$#\" -eq 0 ]; then\n usage;\n exit 1;\nfi\n\necho \"Processing $1 to PID $2\"\nif [ \"$1\" = \"start\" ]; then\n start $2;\nelif [ \"$1\" = \"stop\" ]; then\n stop $2;\nelse\n usage;\nfi;\n[root@nitty-witty sigscripts]#\n<\/pre>\n\n\n\nSample usage:<\/p>\n\n\n\n
[root@nitty-witty sigscripts]# .\/signal.sh\n [stop|start] process_id\n<\/pre>\n\n\n\nWatch video in action: