I have a bash script which will be running a main command, let's say for one hour. I would like to execute another command after a certain time since the main command has been started (at t_x). Something like this:
main starts -------> main ends
|
|
at time t_x, second command is executed
At the moment I have something like this:
mpirun main_command & sleep 1m && second_command
and the problem is that after second command is executed, the main command is killed. Can anyone help me? Thanks!
The first command is failing to lock the console, as another process is also using it. You will need to redirect the standard io pipelines, 0<&- mpirun main_command >/dev/null 2>/dev/null If this still does not work, use shell -c 'mpirun main_command' & sleep 1m;second_command You can use ; instead of &&, unless you need a failing exit code when someone interrupts the sleep.
Related
When running commands from a bash script, does bash always wait for the previous command to complete, or does it just start the command then go on to the next one?
ie: If you run the following two commands from a bash script is it possible for things to fail?
cp /tmp/a /tmp/b
cp /tmp/b /tmp/c
Yes, if you do nothing else then commands in a bash script are serialized. You can tell bash to run a bunch of commands in parallel, and then wait for them all to finish, but doing something like this:
command1 &
command2 &
command3 &
wait
The ampersands at the end of each of the first three lines tells bash to run the command in the background. The fourth command, wait, tells bash to wait until all the child processes have exited.
Note that if you do things this way, you'll be unable to get the exit status of the child commands (and set -e won't work), so you won't be able to tell whether they succeeded or failed in the usual way.
The bash manual has more information (search for wait, about two-thirds of the way down).
add '&' at the end of a command to run it parallel.
However, it is strange because in your case the second command depends on the final result of the first one. Either use sequential commands or copy to b and c from a like this:
cp /tmp/a /tmp/b &
cp /tmp/a /tmp/c &
Unless you explicitly tell bash to start a process in the background, it will wait until the process exits. So if you write this:
foo args &
bash will continue without waiting for foo to exit. But if you don't explicitly put the process in the background, bash will wait for it to exit.
Technically, a process can effectively put itself in the background by forking a child and then exiting. But since that technique is used primarily by long-lived processes, this shouldn't affect you.
In general, unless explicitly sent to the background or forking themselves off as a daemon, commands in a shell script are serialized.
They wait until the previous one is finished.
However, you can write 2 scripts and run them in separate processes, so they can be executed simultaneously. It's a wild guess, really, but I think you'll get an access error if a process tries to write in a file that's being read by another process.
I think what you want is the concept of a subshell. Here's one reference I just googled: http://www.linuxtopia.org/online_books/advanced_bash_scripting_guide/subshells.html
Ive got a script that takes a quite a long time to run, as it has to handle many thousands of files. I want to make this script as fool proof as possible. To this end, I want to check if the user ran the script using nohup and '&'. E.x.
me#myHost:/home/me/bin $ nohup doAlotOfStuff.sh &. I want to make 100% sure the script was run with nohup and '&', because its a very painful recovery process if the script dies in the middle for whatever reason.
How can I check those two key paramaters inside the script itself? and if they are missing, how can I stop the script before it gets any farther, and complain to the user that they ran the script wrong? Better yet, is there way I can force the script to run in nohup &?
Edit: the server enviornment is AIX 7.1
The ps utility can get the process state. The process state code will contain the character + when running in foreground. Absence of + means code is running in background.
However, it will be hard to tell whether the background script was invoked using nohup. It's also almost impossible to rely on the presence of nohup.out as output can be redirected by user elsewhere at will.
There are 2 ways to accomplish what you want to do. Either bail out and warn the user or automatically restart the script in background.
#!/bin/bash
local mypid=$$
if [[ $(ps -o stat= -p $mypid) =~ "+" ]]; then
echo Running in foreground.
exec nohup $0 "$#" &
exit
fi
# the rest of the script
...
In this code, if the process has a state code +, it will print a warning then restart the process in background. If the process was started in the background, it will just proceed to the rest of the code.
If you prefer to bailout and just warn the user, you can remove the exec line. Note that the exit is not needed after exec. I left it there just in case you choose to remove the exec line.
One good way to find if a script is logging to nohup, is to first check that the nohup.out exists, and then to echo to it and ensure that you can read it there. For example:
echo "complextag"
if ( $(cat nohup.out | grep "complextag" ) != "complextag" );then
# various commands complaining to the user, then exiting
fi
This works because if the script's stdout is going to nohup.out, where they should be going (or whatever out file you specified), then when you echo that phrase, it should be appended to the file nohup.out. If it doesn't appear there, then the script was nut run using nohup and you can scold them, perhaps by using a wall command on a temporary broadcast file. (if you want me to elaborate on that I can).
As for being run in the background, if it's not running you should know by checking nohup.
I have a bash script with a loop that calls a hard calculation routine every iteration. I use the results from every calculation as input to the next. I need make bash stop the script reading until every calculation is finished.
for i in $(cat calculation-list.txt)
do
./calculation
(other commands)
done
I know the sleep program, and i used to use it, but now the time of the calculations varies greatly.
Thanks for any help you can give.
P.s>
The "./calculation" is another program, and a subprocess is opened. Then the script passes instantly to next step, but I get an error in the calculation because the last is not finished yet.
If your calculation daemon will work with a precreated empty logfile, then the inotify-tools package might serve:
touch $logfile
inotifywait -qqe close $logfile & ipid=$!
./calculation
wait $ipid
(edit: stripped a stray semicolon)
if it closes the file just once.
If it's doing an open/write/close loop, perhaps you can mod the daemon process to wrap some other filesystem event around the execution? `
#!/bin/sh
# Uglier, but handles logfile being closed multiple times before exit:
# Have the ./calculation start this shell script, perhaps by substituting
# this for the program it's starting
trap 'echo >closed-on-calculation-exit' 0 1 2 3 15
./real-calculation-daemon-program
Well, guys, I've solved my problem with a different approach. When the calculation is finished a logfile is created. I wrote then a simple until loop with a sleep command. Although this is very ugly, it works for me and it's enough.
for i in $(cat calculation-list.txt)
do
(calculations routine)
until [[ -f $logfile ]]; do
sleep 60
done
(other commands)
done
Easy. Get the process ID (PID) via some awk magic and then use wait too wait for that PID to end. Here are the details on wait from the advanced Bash scripting guide:
Suspend script execution until all jobs running in background have
terminated, or until the job number or process ID specified as an
option terminates. Returns the exit status of waited-for command.
You may use the wait command to prevent a script from exiting before a
background job finishes executing (this would create a dreaded orphan
process).
And using it within your code should work like this:
for i in $(cat calculation-list.txt)
do
./calculation >/dev/null 2>&1 & CALCULATION_PID=(`jobs -l | awk '{print $2}'`);
wait ${CALCULATION_PID}
(other commands)
done
I have a program that runs as a daemon, using the C command fork(). It creates a new instance that runs in the background. The main instance exists after that.
What would be the best option to check if the service is running? I'm considering:
Create a file with the process id of the program and check if it's running with a script.
Use ps | grep to find the program in the running proccess list.
Thanks.
I think it will be better to manage your process with supervisord, or other process control system.
Create a cron job that runs every few minutes (or whatever you're comfortable with) and does something like this:
/path/to/is_script_stopped.sh && /path/to/script.sh
Write is_script_stopped.sh using any of the methods that you suggest. If your script is stopped cron will evaluate your script, if not, it won't.
To the question, you gave in the headline:
This simple endless loop will restart yourProgram as soon as it fails:
#!/bin/bash
for ((;;))
do
yourProgram
done
If your program depends on a resource, which might fail, it would be wise to insert a short pause, to avoid, that it will catch all system resources when failing million times per second:
#!/bin/bash
for ((;;))
do
yourProgram
sleep 1
done
To the question from the body of your post:
What would be the best option to check if the service is running?
If your ps has a -C option (like the Linux ps) you would prefer that over a ps ax | grep combination.
ps -C yourProgram
I have a shell script that calls a java jar file and runs an application. There's no way around this, so I have to work with what I have.
When you execute this shell script, it outputs the application status and just sits there (pretty much a console); so when something happens to the program it updates the screen. This is like with any normal non daemonized/backgrounded process. Only way to get out of it is ctrl-c, which then ends the process altogether. I do know that I could get around this by doing path_to_shell_script/script.sh &, which would background it for my session (I could use nohup if I wanted to logout).
My issue is, I just don't know how to put this script into a init script. I have most of the init script written, but when I try to daemonize it, it doesn't work. I've almost got it working, however, when i run the initscript, it actually spans the same "console" on the script, and just sits there until i hit ctrl-c. Here's the line in question:
daemon ${basedir}/$prog && success || failure
The problem is that I can't background just the daemon ${basedir}/$prog part and I think that's where I'm running into the issue. Has anyone been successful at creating an init script FOR a shell script? Also this shell script is not daemonizable (you can background it, but the underlying program does not support a daemonize option, or else I would have just let the application do all the work).
You need to open a subshell to execute it. It also help to redirect its output to a file, or at least /dev/null.
Something like:
#!/bin/bash
(
{ daemon ${basedir}/$prog && success || failure ; } &>/dev/null
) &
exit 0
It work as follows ( list ) & in a background subshell. { list } is a group command, it's used here to capture all the output of your commands and send it to /dev/null.
I have had success with initially detached screen sessions for running things like the half life server and my custom "tail logfile " bash scripts.
To start something in the background:
screen -dmS arbitarySessionName /path/to/script/launchService.sh
To look at the process:
# screen -r arbitrarySessionName
Hope you find this useful, gl!