Running scripts at startup: What's the best way?

My Linode was restarted today due to the power issue in Atlanta. It wasn't a big deal for me, but it did cause confusion when I tried to access it afterward. I usually connect directly to a constantly-running screen session, which wasn't there at the reboot.

This got me thinking: Why not make screen run on startup? My Linode is running Ubuntu 16.04 LTS. When I looked into how to do this, I ran into several options:
* use crontab and add a line with @reboot

  • add an entry to the file /etc/rc.local

  • use the command update-rc.d

I'm not sure which to use and what the differences are. Does anyone have any best practices? I also need to have the script run as a user, not as root, in case that affects how to do things.

Thanks in advance for your insights!

3 Replies

Well, I got something working, so I figured I should answer my question. I'm still interested in hearing if people think there are reasons to do things differently, though. I still don't understand the differences between the various ways I found to run things at startup.

I added the following line to /etc/crontab:

@reboot  user  /home/user/

Here's what's in

screen -S irc -d -m irssi

The irssi command can be replaced by whatever you want running in screen. The -d -m flags are key, though. My first try, I left them out, and though /var/log/syslog showed the script execute, no screen was there on startup. Apparently the normal screen command tries to attach the session to a terminal and quits if it can't find one. screen -d -m starts the screen in detached mode, so it doesn't depend on whether it's being run from a terminal.

At this point, everything ran fine, but screen was opening sh terminals instead of bash, because cron is configured to use sh. Rather than mess with cron, I added this to my .screenrc:

shell "/bin/bash"

I can't give you an opinion on the optimal approach, but I can thank you for the explaining how to do this with cron.


You can also do this with systemd(1)… Construct your service definition; install it in the right place and then

sudo systemctl daemon-reload
sudo systemctl enable <yourservice>

Thereafter, <yourservice> will run at system startup.

To test, you can

sudo systemctl start <yourservice>
sudo systemctl stop <yourservice>
sudo systemctl restart <yourservice>

to make sure <yourservice> starts, stops and restarts gracefully. You should do this before you enable it.

IMHO, this is the best and most reliable way to do this… YMMV.

-- sw

P.S. To do the opposite, you can

sudo systemctl disable <yourservice>

Here's the systemd(1) service I wrote to re-establish my blacklists into my firewall at system boot:

Description=Install blacklists iptables.service firewalld.service ip6tables.service ipset.
service firehol.service



/srv/ids/sbin/iptinstl is the script I wrote to install the blacklists. Whenever the content of the blacklists change while the system is running (every 4 hrs), I can install the updated blacklists by

sudo systemctl restart blacklist


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