crontab

• Schedule processes (cronjobs)
• Processes scheduled by crontab can be hourly, daily, weekly, monthly, etc...

# Schedule a cronjob
# Jobs are per user
# Edit the list of cronjobs in vi
crontab -e
crontab -e -u "bob" # specify another user

# Substitute all entries in crontab
echo "* * * * * root echo 'oi' > /root/oi" | crontab -

# Add entry to crontab
(crontab -l && echo "* * * * *  test") | crontab -

# List all cronjobs
crontab -l

• Cronjob example

22 13 * 3 * echo "Bom dia!" > ~/Downloads/lol.txt

• https://crontab.guru/every-10-minutes

• Minute: 22

• Hour: 13
• Day of the month * (everyday)
• Month: 3 (march)
• Week: * (every week)
• Command: echo "Bom dia!" > ~/Downloads/lol.txt

Cron directories

• Each folder contain scripts that will run at a point in time according to the folder name

# list cron folders
ls -la /etc | grep cron.
ls -la /etc/cron.* # List the content of each one

• /etc/crontab: Store the crontabs created with crontab -e
• /etc/cron.d
• /etc/cron.hourly
• /etc/cron.daily
• /etc/cron.weekly

• /etc/cron.monthly

• The /etc/anacrontab store the configuration about the daily, weekly and monthly jobs

• The /etc/cron.d/0hourly stores the configuration about the hourly job