I have a discord bot running on a raspberry pi that i need to restart every day, I'm trying to do this through crontab but with no luck.
It manages to kill the active screen processes but never starts an instance, not that I can see with "screen -ls" and I can tell that it doesn't create one that I can't see as the bot itself does not come online.
Here is the script:
#!/bin/bash
sudo pkill screen
sleep 2
screen -dmS discordBot
sleep 2
screen -S "discordBot" -X stuff "node discordBot/NEWNEWNEWN\n"
Here is also the crontab:
0 0 * * * /bin/bash /home/admin/discordBot/script.sh
Is it possible to have crontab run a screen session? And if so how?
Previously I tried putting the screen command stright into cron but now I have it in a bash script instead.
If I run the script in the terminal it works perfectly, it’s just cron where it fails. Also replacing "screen" with the full path "/usr/bin/screen" does not change anything.
So the best way of doing it, without investigating the underlying problem would be to create a systemd service and putting a restart command into cron.
/etc/systemd/system/mydiscordbot.service:
[Unit]
Description=A very simple discord bot
[Service]
Type=simple
ExecStart=node /path/to/my/discordBot.js
[Install]
WantedBy=multi-user.target
Now you can run your bot with systemctl start mydiscordbot and can view your logs with journalctl --follow -u mydiscord bot
Now you only need to put
45 2 * * * systemctl restart discordbot
into root's crontab and you should be good to go.
You probably should also write the logs into a logfile, maybe /var/log/mydiscordbot.log, but how and if you do that is up to you.
OLD/WRONG ANSWER:
cron is run with a minimal environment, and depending on your os, /usr/bin/ is probably not in the $PATH var. screen is mostlikely located at /usr/bin/screen, so cron can't run it because it can't find the screen binary. try replacing screen in your script with /usr/bin/screen
But the other question here is: Why does your discord bot need to be restarted every day. I run multiple bots with 100k+ users, and they don't need to be restarted at all. Maybe you should open a new question with the error and some code snippets.
I don't know what os your rpi is running, but I had a similar issue earlier today trying to get vms on a server to launch a terminal and run a python script with crontab. I found a very easily solution to automatically restart it on crashes, and to run something simply in the background. Don't rely on crontab or an init service. If your rpi as an x server running, or anything that can be launched on session start, there is a simple shell solution. Make a bash script like
while :; do
/my/script/to/keep/running/here -foo -bar -baz >> /var/log/myscriptlog 2>&1
done
and then you would start it on .xprofile or some similar startup operation like
/path/to/launcher.sh &
to have it run the background. It will restart automatically everytime it closes if started in something like .xprofile, .xinitrc, or anything ran at startup.
Then maybe make a cronjob to restart the raspberry pi or whatever system is running the script but this script wil restart the service whenever it's closed anyway. Maybe you can put that cronjob on a script but I don't think it would launch the GUI.
Some other things you can do to launch a GUI terminal in my research with cronjob that you can try, though they didn't work for my situation on these custom linux vms, and that I read was a security risk to do this from a cronjob, is you can specify the display.
* * * * * DISPLAY=:0 /your/gui/stuff/here
but you would would need to make sure the user has the right permissions and it's considered an unsafe hack to even do this as far as I have read.
for my issue, I had to launch a terminal that stayed open, and then changed to the directory of a python script and ran the script, so that the local files in directory would be called in the python script. here is a rough example of the "launcher.sh" I called from the startup method this strange linux distro used lol.
#!/bin/sh
while :; do
/usr/bin/urxvt -e /bin/bash -c "cd /path/to/project && python loader.py"
done
Also check this source for process management
https://mywiki.wooledge.org/ProcessManagement
Related
I have a Minecraft Server running on Linux.
I use to start the server, a start.sh file with following content:
(This content starts a screen session and the minecraft server)
screen -S {ScreenSession} java -Xmx2G -Xms2G -jar spigot-1.18.1.jar
If I use /restart ingame, the screen session will end and the server won't start. So I have to go into the Linux Server and start the Minecraft Server again.
My question:
How can I make it so, if I use /restart that the server will restart with a active screen session.
If have tried many things.
I hope someone can help me,
~Kitty Cat Craft
There is multiple way to achieve what you want.
If you have lot of servers, you can use a quick bash script with an auto restart like that:
#!/bin/sh
while true
do
java -Xmx2G -Xms2G -jar spigot-1.18.1.jar --nogui
sleep 5
done
When you will stop, it will wait 5 seconds then restart.
With this, you can use: screen -dmS <screenName> sh myScript.sh which will run the script into another screen. It's usefull when you run it from a script which run lot of server, like that:
screen -dmS srv1 sh srv1.sh
screen -dmS srv2 sh srv2.sh
screen -dmS srv3 sh srv3.sh
You can also, if you have only one server, just firstly use screen -S screenName. Then, when you are in the screen, run the script that restart automatically (the script that I gave at first).
Also, prefer use /stop than /restart, because spigot will try to find the script. And if it success, it will run a second time the same script, and so will have ghost process.
I wrote a POSIX shell script to remind me about my battery life using notify-send and a cronjob, but I'm having problems with DBUS stuff
This is what the script looks like
#!/bin/sh
percent=`upower -i /org/freedesktop/UPower/devices/battery_BAT0 | grep percentage:
notify-send "battery life" "$percent"
It works as intended, and pops up with this notification when called.
I wrote the script because my window manager, i3 lacks a notification system for battery status, so I found myself running out of battery on my laptop even though I was right next to an outlet at home.
Of course; having a script like this is pointlesss unless it's automated to pop up by itself, so after some fiddling, I set up a Cron-job that runs the script every 10 minutes.
This is what the cron-tab looks like:
*/10 * * * * export DISPLAY=:0 ; export DBUS_SESSION_BUS_ADDRESS=a; batterystatus.sh
It works, except that without the little snippet about the DBUS_SESSION_BUS_ADDRESS stuff, for some reason notify-status doesn't work.
So, everything was cool until I rebooted and found that this value used in the cron-tab: unix:abstract=/tmp/dbus-FOSTebXqX5,guid=a7ad198d91d224b8c056efc6615a3610 changes upon boot.
That means that I would have to change the cron-job everytime I boot up my computer so that the script would work. Is there any way around this?
Rather than use crontab, it might be better to use systemd. You can have a systemd user service and timer so that D-Bus has access to the session D-Bus information for session notifications.
I've tested this out using the Python dbus library pydbus as an example bus I'm sure you could use your shell script also.
Python script for getting battery power and posting notifications:
#!/usr/bin/python3
import pydbus
sys_bus = pydbus.SystemBus()
ses_bus = pydbus.SessionBus()
power = sys_bus.get('.UPower', '/org/freedesktop/UPower/devices/battery_BAT0')
notifications = ses_bus.get('.Notifications')
print(power.Percentage)
notifications.Notify('test', 0, 'dialog-information', "Battery Notification!",
f"Percentage: {power.Percentage}%", [], {}, 5000)
Created a user service in /etc/systemd/user/battery.service:
[Unit]
Description=Check for battery percentage
[Service]
Type=dbus
BusName=org.freedesktop.Notifications
ExecStart=/home/thinkabit1/stack_overflow/battery_monitor.py
You can test this works with:
$ systemctl --user start battery.service
To see the status of the service do:
$ systemctl --user status battery.service
To have a timer run this every 10 minutes create /etc/systemd/user/battery.timer
[Unit]
Description=Run battery monitor every 10 minutes
[Timer]
OnBootSec=10min
OnUnitActiveSec=10min
[Install]
WantedBy=timers.target
This can be started with:
$ systemctl --user start battery.timer
To see the status:
$ systemctl --user list-timers
To have it start automatically after reboot use:
systemctl --user enable battery.timer
I would like to make a shutdown-script for my raspberry pi to shut down anothe raspberry pi over ssh.
The script works if it is running itself but at the shutdown routine the ssh command is not executed.
So that I have done until now:
Made the script in /etc/init.d:
#!/bin/sh
# the first thing is to test if the shutdown script is working
echo "bla bla bla " | sudo tee -a /test.txt
ssh pi#10.0.0.98 sudo shutdown -h now
Made it executable
sudo chmod +x /etc/init.d/raspi.sh
Made a symlink to the rc0.d
sudo ln -s /etc/init.d/raspi.sh /etc/rc0.d/S01raspi.sh
Now I know so far that the shutdown script is working outside of the shutdown routing by calling itself and the shutdown symlink I made is also working partially because I see the changes in the test.txt file every time I shut down.
Can anyone help me how to solve my problem?
Have you tried with single quotes?
The first link in Google has it
http://malcontentcomics.com/systemsboy/2006/07/send-remote-commands-via-ssh.html
What about the sudo, how do you solve entering the password?
https://superuser.com/questions/117870/ssh-execute-sudo-command
Please check this or other links on the web that have useful information.
I would have send all this in a comment but I cant yet because of reputation.
I have now got the script running by myself. I do not really know why it is now working but I write it down beneath and maybe someone else can clearifiy it.
I don´t think the first two changes at my system makes a difference but I also write it down. In the meanwhile because I do not managed the script to get working I had made a button to shutdown the system manually. Also I made a script which backs the mysql-database up (which is on the Raspberry Pi which I would like to switch off with the script) and copies the backup to the raspberry pi which should switch of the other raspberry automatically via the shutdown-script. This happens with scp and also for the password is a key generated.
I have also changed my script to get a log-message out of the script.
#!/bin/sh
ssh -t -t pi#10.0.0.99 'sudo shutdown -h now' >> /home/osmc/shutdown.log 2>&1
To get it into the shutdown-routine I used:
sudo update-rc.d raspi-b stop 01 0
I hope somebody can say me why my code now worked on the first day but not on the next few days until now.
I structured a command to suspend or shutdown a remote host over ssh. You may find this useful. This may be used to suspend / shutdown a remote computer without an interactive session and yet not keep a terminal busy. You will need to give permissions to the remote user to shutdown / suspend using sudo without a password. Additionally, the local and remote machines should be set up to SSH without an interactive login. The script is more useful for suspending the machine as a suspended machine will not disconnect the terminal.
local_user#hostname:~$ ssh remote_user#remote_host "screen -d -m sudo pm-suspend"
source: कार्यशाला (Kāryaśālā)
On an Amazon S3 Linux instance, I have two scripts called start_my_app and stop_my_app which start and stop forever (which in turn runs my Node.js application). I use these scripts to manually start and stop my Node.js application. So far so good.
My problem: I also want to set it up such that start_my_app is run whenever the system boots up. I know that I need to add a file inside init.d and I know how to symlink it to the proper directory within rc.d, but I can't figure out what actually needs to go inside the file that I place in init.d. I'm thinking it should be just one line, like, start_my_app, but that hasn't been working for me.
First create your startup script # /home/user/startup.sh, and make it executable
chmod +x /home/user/startup.sh
Then set a crontab for it:
$ crontab -e
#reboot /home/user/startup.sh
Now your your startup.sh script will run at every start.
The file you put in /etc/init.d/ have to be set to executable with:
chmod +x /etc/init.d/start_my_app
As pointed out by #meetamit, if it still does not run you might have to create a symbolic link to the file in /etc/rc.d/
ln -s /etc/init.d/start_my_app /etc/rc.d/
Please note that on the latest versions of Debian, this will not work as your script will have to be LSB compliant (provide at least the following actions: start, stop, restart, force-reload, and status):
https://wiki.debian.org/LSBInitScripts
As a note, you should always use the absolute path to files in your scripts instead of the relative one, it may solve unexpected issues:
/var/myscripts/start_my_app
Finally, make sure that you included the shebang on top of the file:
#!/bin/sh
A simple approach is to add a line in /etc/rc.local :
/PATH/TO/MY_APP &
or if you want to run the command as a special user :
su - USER_FOOBAR -c /PATH/TO/MY_APP &
(the trailing ampersand backgrounds the process and allows the rc.local to continue executing)
If you want a full init script, debian distro have a template file, so :
cp /etc/init.d/skeleton /etc/init.d/your_app
and adapt it a bit.
This is the way I do it on Red Hat Linux systems.
Put your script in /etc/init.d, owned by root and executable. At the top of the script, you can give a directive for chkconfig. Example, the following script is used to start a Java application as user oracle.
The name of the script is /etc/init.d/apex
#!/bin/bash
# chkconfig: 345 99 10
# Description: auto start apex listener
#
case "$1" in
'start')
su - oracle -c "cd /opt/apex ; java -jar apex.war > logs/apex.log 2>logs/apex_error.log &";;
'stop')
echo "put something to shutdown or kill the process here";;
esac
This says that the script must run at levels 3, 4, and 5, and the priority for start/stop is 99 and 10.
Then, as user root you can use chkconfig to enable or disable the script at startup:
chkconfig --list apex
chkconfig --add apex
And you can use service start/stop apex.
Enter cron using sudo:
sudo crontab -e
Add a command to run upon start up, in this case a script:
#reboot sh /home/user/test.sh
Save:
Press ESC then :x to save and exit, or hit ESC then ZZ (that's shift+zz)
Test Test Test:
Run your test script without cron to make sure it actually works.
Make sure you saved your command in cron, use sudo crontab -e
Reboot the server to confirm it all works sudo #reboot
Just have a line added to your crontab..
Make sure the file is executable:
chmod +x /path_to_you_file/your_file
To edit crontab file:
crontab -e
Line you have to add:
#reboot /path_to_you_file/your_file
That simple!
Another option is to have an #reboot command in your crontab.
Not every version of cron supports this, but if your instance is based on the Amazon Linux AMI then it will work.
Edit the rc.local file using nano or gedit editor and add your scripts in it. File path could be /etc/rc.local or /etc/rc.d/rc.local.
sudo nano /etc/rc.local
This is the edit:
#!/bin/sh
/path-to-your-script/your-scipt-name.sh
once done press ctrl+o to update, pressEnter then ctrl+x.
Make the file executable.
sudo chmod 755 /etc/rc.local
Then initiate the rc-local service to run script during boot.
sudo systemctl start rc-local
You can do it :
chmod +x PATH_TO_YOUR_SCRIPT/start_my_app
then use this command
update-rc.d start_my_app defaults 100
Please see this page on Cyberciti.
Many answers on starting something at boot, but often you want to start it just a little later, because your script depends on e.g. networking. Use at to just add this delay, e.g.:
at now + 1 min -f /path/yourscript
You may add this in /etc/rc.local, but also in cron like:
# crontab -e
#reboot at now + 1 min -f /path/yourscript
Isn't it fun to combine cron and at? Info is in the man page man at.
As for the comments that #reboot may not be widely supported, just try it. I found out that /etc/rc.local has become obsolete on distros that support systemd, such as ubuntu and raspbian.
The absolute easiest method if all you want to run is a simple script, (or anything) is if you have a gui to use system > preferences then startup apps.
just browse to the script you want and there you go. (make script executable)
This simple solution worked for me on an Amazon Linux instance running CentOS.
Edit your /etc/rc.d/rc.local file and put the command there. It is mentioned in this file that it will be executed after all other init scripts. So be careful in that regards. This is how the file looks for me currently.. Last line is the name of my script.
Create your own /init executable
This is not what you want, but it is fun!
Just pick an arbitrary executable file, even a shell script, and boot the kernel with the command line parameter:
init=/path/to/myinit
Towards the end of boot, the Linux kernel runs the first userspace executable at the given path.
Several projects provide popular init executables used by major distros, e.g. systemd, and in most distros init will fork a bunch of processes used in normal system operation.
But we can hijack /init it to run our own minimal scripts to better understand our system.
Here is a minimal reproducible setup: https://github.com/cirosantilli/linux-kernel-module-cheat/tree/f96d4d55c9caa7c0862991025e1291c48c33e3d9/README.md#custom-init
I refered to this blog, always sound a good choice
https://blog.xyzio.com/2016/06/14/setting-up-a-golang-website-to-autorun-on-ubuntu-using-systemd/
vim /lib/systemd/system/gosite.service
Description=A simple go website
ConditionPathExists=/home/user/bin/gosite
[Service]
Restart=always
RestartSec=3
ExecStart=/home/user/bin/gosite
[Install]
WantedBy=multi-user.target
systemctl enable gosite.service
multi ways to finish it:
crontab
rc.local
init.d
systemd
For Debian 9 see https://askubuntu.com/questions/228304/how-do-i-run-a-script-at-start-up. It is helped me. Short version for Debian 9:
add commands (as root) to /etc/rc.local
/path_to_file/filename.sh || exit 1 # Added by me
exit 0
Probably, /path_to_file/filename.sh should be executable (I think so).
In Lubuntu I had to deal with the opposite situation. Skype start running after booting and I found in ~/.config/autostart/ the file skypeforlinux.desktop. The content of the file is as follows:
[Desktop Entry]
Name=Skype for Linux
Comment=Skype Internet Telephony
Exec=/usr/bin/skypeforlinux
Icon=skypeforlinux
Terminal=false
Type=Application
StartupNotify=false
X-GNOME-Autostart-enabled=true
Deleting this file helped me.
Here is a simpler method!
First: write a shell script and save it a .sh
here is an example
#!/bin/bash
Icoff='/home/akbar/keyboardONOFF/icon/Dt6hQ.png'
id=13
fconfig=".keyboard"
echo "disabled" > $fconfig
xinput float $id
notify-send -i $Icoff "Internal Keyboard disabled";
this script will disable the internal keyboard at startup.
Second: Open the application " Startup Application Preferences"
enter image description here
enter image description here
Third: click Add.
fourth: in the NAME section give a name.
fifth: In the command section browse to your .sh .
sixth: edit your command section to:
bash <space> path/to/file/<filename>.sh <space> --start
seventh: click Add. Thats it! Finished!
Now confirm by rebooting your pc.
cheers!
Add your script to /etc/init.d/ directory
Update your rc run-levels:
$ update-rc.d myScript.sh defaults NN where NN is the order in which it should be executed. 99 for example will mean it would be run after 98 and before 100.
Painless, easiest and the most universal method is simply
executing it with ~.bash_profile or ~.profile (if you don't have bash_profile file).
Just add the execution command at the bottom of that file and it will be executed when system started.
I have this one at the bottom an example;
~\Desktop\sound_fixer.sh
Working with Python 3 microservices or shell; using Ubuntu Server 18.04 (Bionic Beaver) or Ubuntu 19.10 (Eoan Ermine) or Ubuntu 18.10 (Cosmic Cuttlefish) I always do like these steps, and it worked always too:
Creating a microservice called p example "brain_microservice1.service" in my case:
$ nano /lib/systemd/system/brain_microservice1.service
Inside this new service that you are in:
[Unit]
Description=brain_microservice_1
After=multi-user.target
[Service]
Type=simple
ExecStart=/usr/bin/python3.7 /root/scriptsPython/RUN_SERVICES/microservices /microservice_1.py -k start -DFOREGROUND
ExecStop=/usr/bin/python3.7 /root/scriptsPython/RUN_SERVICES/microservices/microservice_1.py -k graceful-stop
ExecReload=/usr/bin/python3.7 /root/scriptsPython/RUN_SERVICES/microservices/microservice_1.py -k graceful
PrivateTmp=true
LimitNOFILE=infinity
KillMode=mixed
Restart=on-failure
RestartSec=5s
[Install]
WantedBy=multi-user.target
Give the permissions:
$ chmod -X /lib/systemd/system/brain_microservice*
$ chmod -R 775 /lib/systemd/system/brain_microservice*
Give the execution permission then:
$ systemctl daemon-reload
Enable then, this will make then always start on startup
$ systemctl enable brain_microservice1.service
Then you can test it;
$ sudo reboot now
Finish = SUCCESS!!
This can be done with the same body script to run shell, react ... database startup script ... any kind os code ... hope this help u...
...
For some people, this will work:
You could simply add the following command into System → Preferences → Startup Applications:
bash /full/path/to/your/script.sh
I'm trying to ensure a script remains running on a development server. It collates stats and provides a web service so it's supposed to persist, yet a few times a day, it dies off for unknown reasons. When we notice we just launch it again, but it's a pain in the rear and some users don't have permission (or the knowhow) to launch it up.
The programmer in me wants to spend a few hours getting to the bottom of the problem but the busy person in me thinks there must be an easy way to detect if an app is not running, and launch it again.
I know I could cron-script ps through grep:
ps -A | grep appname
But again, that's another hour of my life wasted on doing something that must already exist... Is there not a pre-made app that I can pass an executable (optionally with arguments) and that will keep a process running indefinitely?
In case it makes any difference, it's Ubuntu.
I have used a simple script with cron to make sure that the program is running. If it is not, then it will start it up. This may not be the perfect solution you are looking for, but it is simple and works rather well.
#!/bin/bash
#make-run.sh
#make sure a process is always running.
export DISPLAY=:0 #needed if you are running a simple gui app.
process=YourProcessName
makerun="/usr/bin/program"
if ps ax | grep -v grep | grep $process > /dev/null
then
exit
else
$makerun &
fi
exit
Then add a cron job every minute, or every 5 minutes.
Monit is perfect for this :)
You can write simple config files which tell monit to watch e.g. a TCP port, a PID file etc
monit will run a command you specify when the process it is monitoring is unavailable/using too much memory/is pegging the CPU for too long/etc. It will also pop out an email alert telling you what happened and whether it could do anything about it.
We use it to keep a load of our websites running while giving us early warning when something's going wrong.
-- Your faithful employee, Monit
Notice: Upstart is in maintenance mode and was abandoned by Ubuntu which uses systemd. One should check the systemd' manual for details how to write service definition.
Since you're using Ubuntu, you may be interested in Upstart, which has replaced the traditional sysV init. One key feature is that it can restart a service if it dies unexpectedly. Fedora has moved to upstart, and Debian is in experimental, so it may be worth looking into.
This may be overkill for this situation though, as a cron script will take 2 minutes to implement.
#!/bin/bash
if [[ ! `pidof -s yourapp` ]]; then
invoke-rc.d yourapp start
fi
If you are using a systemd-based distro such as Fedora and recent Ubuntu releases, you can use systemd's "Restart" capability for services. It can be setup as a system service or as a user service if it needs to be managed by, and run as, a particular user, which is more likely the case in OP's particular situation.
The Restart option takes one of no, on-success, on-failure, on-abnormal, on-watchdog, on-abort, or always.
To run it as a user, simply place a file like the following into ~/.config/systemd/user/something.service:
[Unit]
Description=Something
[Service]
ExecStart=/path/to/something
Restart=on-failure
[Install]
WantedBy=graphical.target
then:
systemctl --user daemon-reload
systemctl --user [status|start|stop|restart] something
No root privilege / modification of system files needed, no cron jobs needed, nothing to install, flexible as hell (see all the related service options in the documentation).
See also https://wiki.archlinux.org/index.php/Systemd/User for more information about using the per-user systemd instance.
I have used from cron "killall -0 programname || /etc/init.d/programname start". kill will error if the process doesn't exist. If it does exist, it'll deliver a null signal to the process (which the kernel will ignore and not bother passing on.)
This idiom is simple to remember (IMHO). Generally I use this while I'm still trying to discover why the service itself is failing. IMHO a program shouldn't just disappear unexpectedly :)
Put your run in a loop- so when it exits, it runs again... while(true){ run my app.. }
I couldn't get Chris Wendt solution to work for some reason, and it was hard to debug. This one is pretty much the same but easier to debug, excludes bash from the pattern matching. To debug just run: bash ./root/makerun-mysql.sh. In the following example with mysql-server just replace the value of the variables for process and makerun for your process.
Create a BASH-script like this (nano /root/makerun-mysql.sh):
#!/bin/bash
process="mysql"
makerun="/etc/init.d/mysql restart"
if ps ax | grep -v grep | grep -v bash | grep --quiet $process
then
printf "Process '%s' is running.\n" "$process"
exit
else
printf "Starting process '%s' with command '%s'.\n" "$process" "$makerun"
$makerun
fi
exit
Make sure it's executable by adding proper file permissions (i.e. chmod 700 /root/makerun-mysql.sh)
Then add this to your crontab (crontab -e):
# Keep processes running every 5 minutes
*/5 * * * * bash /root/makerun-mysql.sh
The supervise tool from daemontools would be my preference - but then everything Dan J Bernstein writes is my preference :)
http://cr.yp.to/daemontools/supervise.html
You have to create a particular directory structure for your application startup script, but it's very simple to use.
first of all, how do you start this app? Does it fork itself to the background? Is it started with nohup .. & etc? If it's the latter, check why it died in nohup.out, if it's the first, build logging.
As for your main question: you could cron it, or run another process on the background (not the best choice) and use pidof in a bashscript, easy enough:
if [ `pidof -s app` -eq 0 ]; then
nohup app &
fi
You could make it a service launched from inittab (although some Linuxes have moved on to something newer in /etc/event.d). These built in systems make sure your service keeps running without writing your own scripts or installing something new.
It's a job for a DMD (daemon monitoring daemon). there are a few around; but I usually just write a script that checks if the daemon is running, and run if not, and put it in cron to run every minute.
Check out 'nanny' referenced in Chapter 9 (p197 or thereabouts) of "Unix Hater's Handbook" (one of several sources for the book in PDF).
A nice, simple way to do this is as follows:
Write your server to die if it can't listen on the port it expects
Set a cronjob to try to launch your server every minute
If it isn't running it'll start, and if it is running it won't. In any case, your server will always be up.
I think a better solution is if you test the function, too. For example, if you had to test an apache, it is not enough only to test, if "apache" processes on the systems exist.
If you want to test if apache OK is, then try to download a simple web page, and test if your unique code is in the output.
If not, kill the apache with -9 and then do a restart. And send a mail to the root (which is a forwarded mail address to the roots of the company/server/project).
It's even simplier:
#!/bin/bash
export DISPLAY=:0
process=processname
makerun="/usr/bin/processname"
if ! pgrep $process > /dev/null
then
$makerun &
fi
You have to remember though to make sure processname is unique.
One can install minutely monitoring cronjob like this:
crontab -l > crontab;echo -e '* * * * * export DISPLAY=":0.0" && for
app in "eiskaltdcpp-qt" "transmission-gtk" "nicotine";do ps aux|grep
-v grep|grep "$app";done||"$app" &' >> crontab;crontab crontab
disadvantage is that the app names you enter have to be found in ps aux|grep "appname" output and at same time being able to be launched using that name: "appname" &
also you can use the pm2 library.
sudo apt-get pm2
And if its a node app can install.
Sudo npm install pm2 -g
them can run the service.
linux service:
sudo pm2 start [service_name]
npm service app:
pm2 start index.js