Suppose I saw a process X in output of top or ps, I want to know which shell script started it, is there a easy way?
I think it's too stupid to find/grep the whole harddisk.
EDIT: I just want to find the script file name and path, not the command line which start the process.
In ps, there is the ability to view ppid, the parent process id. That will indicate the process that started the child. For a prettier display, check out pstree.
Related
I saw >_ in bash shell icon in mac and was wondering what it will do.
I tried performing the command but I was not able to figure out what happened. My command prompt silently came again.
It should be doing something, that's why it is in the icon for terminal.
Do anyone know what it does and can it be used for something?
Running >_ will successfully run (nothing), redirected to a file named _. It's not terribly useful, but that's what it does. The most useful empty redirection I've seen is to empty the contents of a file with it:
> /var/log/app.log
which, if app.log is not open by another process, will result in /var/log/app.log being empty.
Say you have a shell command like
cat file1 | ./my_script
Is there any way from inside the 'my_script' command to detect the command run first as the pipe input (in the above example cat file1)?
I've been digging into it and so far I've not found any possibilities.
I've been unable to find any environment variables set in the process space of the second command recording the full command line, the command data the my_script commands sees (via /proc etc) is just _./my_script_ and doesn't include any information about it being run as part of a pipe. Checking the process list from inside the second command even doesn't seem to provide any data since the first process seems to exit before the second starts.
The best information I've been able to find suggests in bash in some cases you can get the exit codes of processes in the pipe via PIPESTATUS, unfortunately nothing similar seems to be present for the name of commands/files in the pipe. My research seems to be saying it's impossible to do in a generic manner (I can't control how people decide to run my_script so I can't force 3rd party pipe replacement tools to be used over build in shell pipes) but it just at the same time doesn't seem like it should be impossible since the shell has the full command line present as the command is run.
(update adding in later information following on from comments below)
I am on Linux.
I've investigated the /proc/$$/fd data and it almost does the job. If the first command doesn't exit for several seconds while piping data to the second command can you read /proc/$$/fd/0 to see the value pipe:[PIPEID] that it symlinks to. That can then be used to search through the rest of the /proc//fd/ data for other running processes to find another process with a pipe open using the same PIPEID which gives you the first process pid.
However in most real world tests I've done of piping you can't trust that the first command will stay running long enough for the second one to have time to locate it's pipe fd in /proc before it exits (which removes the proc data preventing it being read). So if this method will return any information is something I can't rely on.
So, I need to run a program, not keep track of its PID (in memory, at least), and later kill that program. Any ideas? My immediate thought was to tag the process with something I could find later, but that seems a bust. My next thought was to store on disk the PID, but I've no idea what the convention for that sort of thing is. Any ideas? Thanks!
Your program can create a directory under /var/run/ to store such files. For instance, if your program is myprog it might store its PID on startup in
/var/run/myprog/PID
If your program could have multiple instances running at the same time, you might use the PID itself in the file name, along with its startup time, to ensure a unique file name for each instance.
/var/run/myprog/201410302306.1283.pid
(Note that if you use the PID in the file name, it's up to you if you actually write the PID in the file itself; an empty file would suffice.)
The most straight forward (and common case) is, as you and chepner already mentioned, to store it in a pid file. For this:
If it's a system wide programm:
/var/run/prog.pid
If it's a system installed program that might be run multiple times:
/var/run/prog/prog_instance.pid
If it's a user local program:
$HOME/.prog/prog.pid
Other options might be to use pgrep for finding it as long as you can uniquely define the calling command. For example pass a dummy argument not used and use it for retrieval:
$ prog.sg --instance_1234 &
$ pgrep -f -- '--instance_1234'
3523
you can use start-stop-daemon to start a program and kill it later. It has a lot of options to find the programm, the most usefull is the --pid that stores and retrive the pid from a file in filesystem, usually in /var/run (pay attention to file system privileges to write in it).
See the man pages for more tips.
I'm quite familiar with Dir.chdir("/xyz")
Unfortunately, this changes the directory of the process, but not actually the directory of the user. I'll make the following example to illustrate my need.
$~/: ruby my_script.rb
CHANGING TO PATH FOR USER NOT SCRIPT
$/Projects/Important/Path: pwd
$/Projects/Important/Path
See? I need the script to change the user's path. Performing system/backticks/Dir.chdir all adjust the process path, and end with the user sitting where they started, instead of the path I want them.
From what I've read exec was the way to go, since it takes over the existing process... but to no avail.
You can't, but you can do something which might be good enough. You can invoke another shell from ruby:
Dir.chdir("/xyz")
system("bash")
Running this will create a new bash process, which will start in the /xyz directory. The downside is that changing this process will bring you back to the ruby script, and assuming it ends right away - back to the bash process that started the ruby script.
Another hack that might work is to use the prompt as a hackish hook that will be called after each command. In the ruby script, you can write the new directory's path somewhere that can be read from both bash and ruby(for example a file - but not an environment variable!). In the PROMPT_COMMAND function, you check that file and cd to what's written there. Just make sure you delete that file, so you don't get automatically cded there after every command you run.
I am on UBUNTU 12.04.
I have a shell script that logs the output of a certain processes. The process being logged changes depending on the parent shell script that called the logging script. I would like to write the output of this logging to a file on disk, but am having trouble naming the file.
I would love to name it according to the parent script's own name. Unfortunately I have absolutely no idea how to get that name from script. I imagine that the best way to do that would be to extract the parent PID ($PPID), and then use that to find the script name, but I also don't know how to do that.
Instead of jumping through hoops to do this, just have the parent open the log on say FD4. Then whenever you need to log, just write to FD4.
# parent script
exec 4>> parent.log
# child script
echo "Log me!" >&4