I'm trying to write a bash script.
The script should check if the MC server is running. If it crashed or stopped it will start the server automatically.
I'll use crontab to run the script every minute. I think I can run it every second it won't stress the CPU too much. I also would like to know when was the server restarted. So I'm going to print the date to the "RestartLog" file.
This is what I have so far:
#!/bin/sh
ps auxw | grep start.sh | grep -v grep > /dev/null
if [ $? != 0 ]
then
cd /home/minecraft/minecraft/ && ./start.sh && echo "Server restarted on: $(date)" >> /home/minecraft/minecraft/RestartLog.txt > /dev/null
fi
I'm just started learning Bash and I'm not sure if this is the right way to do it.
The use of cron is possible, there are other (better) solutions (monit, supervisord etc.). But that is not the question; you asked for "the right way". The right way is difficult to define, but understanding the limits and problems in your code may help you.
Executing with normal cron will happen at most once per minute. That means that you minecraft server may be down 59 seconds before it is restarted.
#!/bin/sh
You should have the #! at the beginning of the line. Don't know if this is a cut/paste problem, but it is rather important. Also, you might want to use #!/bin/bash instead of #!/bin/sh to actually use bash.
ps auxw | grep start.sh | grep -v grep > /dev/null
Some may suggest to use ps -ef but that is a question of taste. You may even use ps -ef | grep [s]tart.sh to prevent using the second grep. The main problem however with this line is that that you are parsing the process-list for a fairly generic start.sh. This may be OK if you have a dedicated server for this, but if there are more users on the server, you run the risk that someone else runs a start.sh for something completely different.
if [ $? != 0 ]
then
There was already a comment about the use of $? and clean code.
cd /home/minecraft/minecraft/ && ./start.sh && echo "Server restarted on: $(date)" >> /home/minecraft/minecraft/RestartLog.txt > /dev/null
It is a good idea to keep a log of the restarts. In this line, you make the execution of the ./start.sh dependent on the fact that the cd succeeds. Also, the echo only gets executed after the ./start.sh exists.
So that leaves me with a question: does start.sh keep on running as long as the server runs (in that case: the ps-test is ok, but the && echo makes no sense, or does start.sh exit while leaving the minecraft-server in the background (in that case the ps-grep won't work correctly, but it makes sense to echo the log record only if start.sh exits correctly).
fi
(no remarks for the fi)
If start.sh blocks until the server exists/crashes, you'd be better off to simply restart it in an infinite loop without the involvement of cron. Simply type in a console (or put into another script):
#!/bin/bash
cd /home/minecraft/minecraft/
while sleep 3; do
echo "$(date) server (re)start" >> restart.log
./start.sh # blocks until server crashes
done
But if it doesn't block (i.e. if start.sh starts the server and then returns, but the server keeps running), you would need to implement a different check to verify if the server is actually still running, other than ps|grep start.sh
PS: To kill the infinite loop you have to Ctrl+C twice: Once to stop ./start.sh and once to exit from the immediate sleep.
You can use monit for this task. See docu. It is available on most linux distributions and has a straightforward config. Find some examples in this post
For your app it will look something like
check process minecraftserver
matching "start.sh"
start program = "/home/minecraft/minecraft/start.sh"
stop program = "/home/minecraft/minecraft/stop.sh"
I wrote this answer because sometimes the most efficient solution is already there and you don't have to code anything. Also follow the suggestions of William Pursell and use the init system of your OS (systemd,upstart,system-v,etc.) to host your scripts.
Find more:
Shell Script For Process Monitoring
Related
Due to some issues I wont elaborate here to not waste time, I made a bash script which will ping google every 10 minutes and if there is a response it will keep the loop running and if not then the PC will restart. After a lot of hurdle I have been able to make the script and also make it start on bootup. However the issue is that i want to see the results on the terminal, meaning I want to keep monitoring it but the terminal does not open on bootup. But it does open if I run it as ./net.sh.
The script is running on startup, that much I know because I use another script to open an application and it works flawlessly.
My system information
NAME="Linux Mint"
VERSION="18.3 (Sylvia)"
ID=linuxmint
ID_LIKE=ubuntu
PRETTY_NAME="Linux Mint 18.3"
VERSION_ID="18.3"
HOME_URL="http://www.linuxmint.com/"
SUPPORT_URL="http://forums.linuxmint.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/linuxmint/"
VERSION_CODENAME=sylvia
UBUNTU_CODENAME=xenial
The contents of my net.sh bash script are
#! /bin/bash
xfce4-terminal &
sleep 30
while true
do
ping -c1 google.com
if [ $? == 0 ]; then
echo "Ping Sucessful. The Device will Continue Operating"
sleep 600
else
systemctl reboot
fi
done
I have put the scripts in /usr/bin and inserted the scripts for startup at boot in /etc/rc.local
So I did some further research and with help from reddit I realized that the reason I couldnt get it to show on terminal was because the script was starting on bootup but I needed it to start after user login. So I added the script on startup application (which can be found searching on start menu if thats whats it called). But it was still giving issues so I divided the script in two parts.
I put the net.sh script on startup and directed that script to open my main script which i named net_loop.sh
This is how the net.sh script looks
#! /bin/bash
sleep 20
xfce4-terminal -e usr/bin/net_loop.sh
And the net_loop.sh
#! /bin/bash
while true
do
ping -c1 google.com
if [ $? == 0 ]; then
echo "Ping Sucessful. The Device will Continue Operating"
sleep 600
else
systemctl reboot
fi
done
The results are the results of the net_loop.sh script are open in another terminal.
Note: I used help from this thread
If minute interval is usable why not use "cron" to start your?
$> crontab –e
or
$> sudo crontab –e
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've been experimenting with Pis for a little while now and am close to completing my first project, I have all the bits working but I'm struggling to put them all together into an automated process.
Basically I have a Pi setup to run a fbi slideshow from a specific folder and I want it to constantly be looking for a pre established Wifi network and when it finds this network it needs to run an update script. I've got these two bits working.
From here, I want the Pi to be turned on and load straight into fbi whilst running the checking script in the background, if the checking script finds the Wifi network then it will run as normal (preferably without ending the slideshow) and when it's done fbi should have an updated selection of images to run (if a restart of fbi is necessary then so be it).
I'm coming up short on achieving this. I can run one script or the other, and if I automate the checking script (cron hasn't worked though I dare say I'm doing something wrong) with rc.local it just gets stuck in a checking loop before login, which kinda makes sense given the script.
Here's the monitoring script:
#!/bin/bash
while true ; do
if ifconfig wlan0 | grep -q "inet addr:" ; then
echo "Wifi connected!"
echo "Initiating Grive sync!"
(cd /home/pi/images/; ./grive -s Pi_Test -V)
sleep 60
else
echo "Wifi disconnected! Attempting to reconnect now."
ifup --force wlan0
sleep 10
fi
done
and in case it's relevant, here's the command the run the fbi slideshow:
fbi -noverbose -a -t 10 -u /home/pi/images/Pi_Test/*.jpg
I do not have a Pi but I have used cron on my VPS which is running a CentOS, but the overall procedure should be similar.
To have some script to be executed by cron, you need to:
Edit /etc/cron.allow
You need to add in your user id to this file so that you can use crontab.
crontab -e
Use this command to add rules you want to fire.
From your description, it seems to me that you already know the syntax to add rules into cron table.
After that, you can use crontab -l to verify your change.
As for stuck at before login, that is very likely due to the while loop. You might want to get rid of the while and sleep because cron is helping you out by invoking your script periodically.
Therefore the following should not suffer from the stuck issue.
if ifconfig wlan0 | grep -q "inet addr:" ; then
echo "Wifi connected!"
echo "Initiating Grive sync!"
(cd /home/pi/images/; ./grive -s Pi_Test -V)
else
echo "Wifi disconnected! Attempting to reconnect now."
ifup --force wlan0
fi
The trick instead, is to have some line similar to this in your cron table
*/1 * * * * /home/David_Legassick/test.sh
The */1 asks cron to call your script test.sh every minute.
I'm running two tests on a remote server, here is the command I used several hours ago:
% ./test1.sh; ./test2.sh
The two tests are supposed to run one by one.If the second runs before the first completes, everything will be in ruin, and I'll have to restart the whole procedure.
The dilemma is, these two tasks cost too many hours to complete, and when I prepare to logout the server and wait for the result. I don't know how to switch both of them to background... If I use Ctrl+Z, only the first task will be suspended, while the second starts doing nothing useful while wiping out current data.
Is it possible to switch both of them to background, preserving their orders? Actually I should make these two tasks in the same process group like (./test1.sh; ./test2.sh) &, but sadly, the first test have run several hours, and it's quite a pity to restart the tests.
An option is to kill the second test before it starts, but is there any mechanism to cope with this?
First rename the ./test2.sh to ./test3.sh. Then do [CTRL+Z], followed by bg and disown -h. Then save this script (test4.sh):
while :; do
sleep 5;
pgrep -f test1.sh &> /dev/null
if [ $? -ne 0 ]; then
nohup ./test3.sh &
break
fi
done
then do: nohup ./test4.sh &.
and you can logout.
First, screen or tmux are your friends here, if you don't already work with them (they make remote machine work an order of magnitude easier).
To use conditional consecutive execution you can write:
./test1.sh && ./test2.sh
which will only execute test2.sh if test1.sh returns with 0 (conventionally meaning: no error). Example:
$ true && echo "first command was successful"
first command was successful
$ ! true && echo "ain't gonna happen"
More on control operators: http://www.humbug.in/docs/the-linux-training-book/ch08s01.html
i am using shell script to monitor the working of a php script. My aim is that this php script should not sleep / terminated and must always be running.The code i used is -
ps aux | grep -v grep | grep -q $file || ( nohup php -f $file -print > /var/log/file.log & )
now this idea would not work for cases if the php script got terminated(process status code T). Any idea to handle that case. can such processes be killed permanently and then restarted.
How about just restarting the php interpreter when it dies?
while true ; do php -f $file -print >> /var/log/file.log ; done
Of course, someone could send the script a SIGSTOP, SIGTSTP, SIGTTIN, SIGTTOU to cause it to hang, but perhaps that person has a really good reason. You can block them all except SIGSTOP, so maybe that's alright.
Or if the script does something like call read(2) on a device or socket that will never return, this won't really ensure the 'liveness' of your script. (But then you'd use non-blocking IO to prevent this situation, so that's covered.)
Oh yes, you could also stuff it into your /etc/inittab. But I'm not giving you more than a hint about this one, because I think it is probably a bad idea.
And there are many similar tools that already exist: daemontools and Linux Heartbeat are the first two to come to mind.
If the script is exiting after it's been terminater, or if it crashes out, and needs to be restarted, a simple shell script can take care of that.
#!/bin/bash
# runScript.sh - keep a php script running
php -q -f ./cli-script.php -- $#
exec $0 $#;
The exec $0 re-runs the shell script, with the parameters it was given.
To run in the background you can nohup runScript.sh or run it via init.d scripts, upstart, runit or supervisord, among others.