cloud engineer
How to add bash scripts on startup.
update-rc.d
sudo cp /path/to/yourscript.sh /etc/init.d/yourscript.sh sudo update-rc.d /etc/init.d/yourscript.sh defaults chmod +x /etc/init.d/yourscript.sh |
sudo cp /path/to/yourscript.sh /etc/init.d/yourscript.sh sudo update-rc.d /etc/init.d/yourscript.sh defaults chmod +x /etc/init.d/yourscript.sh
Root Crontab
sudo crontab -e @reboot /path/to/yourscript.sh |
sudo crontab -e @reboot /path/to/yourscript.sh
How to display IP address and Instance ID on web page behind a AWS load balancer.
Add these 2 commands in crontab. The job runs every 5 mins.
*/5 * * * * /usr/bin/curl http://169.254.169.254/latest/meta-data/instance-id > /var/www/html/id.txt */5 * * * * /usr/bin/curl http://169.254.169.254/latest/meta-data/public-ipv4 > /var/www/html/ip.txt |
*/5 * * * * /usr/bin/curl http://169.254.169.254/latest/meta-data/instance-id > /var/www/html/id.txt */5 * * * * /usr/bin/curl http://169.254.169.254/latest/meta-data/public-ipv4 > /var/www/html/ip.txt
You can view on the site.
# your domain http://yourdomain.com/ip.txt http://yourdomain.com/id.txt # your server ip address http://1.1.1.1/ip.txt http://1.1.1.1/id.txt |
# your domain http://yourdomain.com/ip.txt http://yourdomain.com/id.txt # your server ip address http://1.1.1.1/ip.txt http://1.1.1.1/id.txt
If you want to change the crontab editor, run the following:
$ select-editor |
$ select-editor
Choose one.
How to load crontab from file.
crontab /path/to/file.txt |
crontab /path/to/file.txt
Save crontab to a file.
crontab -l > /path/to/file.txt |
crontab -l > /path/to/file.txt
Here’s a neat command to append a job to a crontab within a Bash script.
crontab -l | { cat; echo "0 1 * * * /dir/script.sh > /logs/script.cronlog 2>&1"; } | crontab - |
crontab -l | { cat; echo "0 1 * * * /dir/script.sh > /logs/script.cronlog 2>&1"; } | crontab -
To validate, perform crontab -l to see if your changes are there.
crontab -l |
crontab -l
I’m running a “source” command inside a Bash script. The script is running fine on its own, but when I try running it inside a crontab, it doesn’t work. I’m using the source command just to load variables in a file, so I don’t have to edit multiple files. As it turns out, the regular shell in crontab does not quite understand the source command, and it’s the very reason the script fails. Here’s an example.
source /home/user/server.conf |
source /home/user/server.conf
I ended up removing the source line, and hardcoding the variables instead of loading it from a file.
server="servername" |
server="servername"