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Unix Advanced: Difference between revisions
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Processes | Processes | ||
A process is a program that runs when you execute a command in UNIX. You can have more than one process running at a time, which obviously means you can have more than one program running at a time. "How can this be Conor!?" you shout at me. I cover my ears and respond that you can run some programs in the background or you can put some programs on hold while you do something else equally crazy. And here's how you do all this magic UNIX stuff! | A process is a program that runs when you execute a command in UNIX. You can have more than one process running at a time, which obviously means you can have more than one program running at a time. "How can this be, Conor!?" you shout at me. I cover my ears and respond that you can run some programs in the background or you can put some programs on hold while you do something else equally crazy. And here's how you do all this magic UNIX stuff! | ||
== Suspending a Process == | == Suspending a Process == | ||
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cokane 68730 0.0 0.3 1620 1324 pi T 5:36PM 0:00.02 slrn | cokane 68730 0.0 0.3 1620 1324 pi T 5:36PM 0:00.02 slrn | ||
cokane 68741 0.0 0.0 388 220 pi R+ 5:36PM 0:00.00 ps -u | cokane 68741 0.0 0.0 388 220 pi R+ 5:36PM 0:00.00 ps -u | ||
prompt$ ps | prompt$ ps | ||
PID TT STAT TIME COMMAND | PID TT STAT TIME COMMAND | ||
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68730 pi T 0:00.02 slrn | 68730 pi T 0:00.02 slrn | ||
68749 pi R+ 0:00.00 ps | 68749 pi R+ 0:00.00 ps | ||
prompt$ kill -SIGKILL 68730 | prompt$ kill -SIGKILL 68730 | ||
[1] + killed slrn | [1] + killed slrn | ||
prompt$ | prompt$ | ||
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You see in the above example that when a process gets killed (or finishes itself), the shell will print that the process has finished or has been killed. In the above example you can see that it shows the job number in square brackets, then the reason the process returned (that it was killed) and the name of the process. | You see in the above example that when a process gets killed (or finishes itself), the shell will print that the process has finished or has been killed. In the above example you can see that it shows the job number in square brackets, then the reason the process returned (that it was killed) and the name of the process. | ||
Signals | |||
== Signals == | |||
Now I will (attempt to) explain signals in UNIX... | Now I will (attempt to) explain signals in UNIX... | ||
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Below I will list some of the most common signals and what they're used for. I reserve the right to be very wrong about some of them :o) | Below I will list some of the most common signals and what they're used for. I reserve the right to be very wrong about some of them :o) | ||
*SIGKILL As explained already... to kill a process | *SIGKILL | ||
As explained already... to kill a process | |||
*SIGTERM Similar to SIGKILL but it won't kill the process straight away. | *SIGTERM | ||
Similar to SIGKILL but it won't kill the process straight away. | |||
*SIGSTOP This is the signal which suspends a process.. | *SIGSTOP | ||
This is the signal which suspends a process.. | |||
*SIGSTP Similar to SIGSTOP, this is the signal that pressing | *SIGSTP | ||
Similar to SIGSTOP, this is the signal that pressing CTRL + Z sends. | |||
*SIGCONT The signal sent to continue a suspended process. | *SIGCONT | ||
The signal sent to continue a suspended process. | |||
*SIGTTOU This occurs when a process running in the background attempts | *SIGTTOU | ||
This occurs when a process running in the background attempts to write to the terminal. The process gets suspended. | |||
*SIGTTIN As above except occurs when process tries to read input | *SIGTTIN | ||
As above except occurs when process tries to read input from terminal. | |||
*SIGHUP The "hang up" signal, nowadays sending this to a process | *SIGHUP | ||
The "hang up" signal, nowadays sending this to a process will cause the process (if it's a daemon) to re-read its configuration files without you having to restart the process itself. | |||
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There ends my sucky sig explanation ;o) | There ends my sucky sig explanation ;o) | ||
Hopefully you've found this tutorial a bit helpful and have maybe learnt something as well from it as well. | |||
== Links == | |||
[[Unix Intro]] - basic Unix commands, just in case you forgot them or something... | |||
[[Helpdesk]] - more tutorials! | |||
[[Category:Helpdesk]] | |||