Exercise

Backing Up Documents Nightly Exercise

Task

Back up your documents every night at 2 a.m., with each run writing to its own timestamped directory so one backup never overwrites another. Prove the schedule works before you trust it.

Host: servera
Back up: /home/student/Documents
Destination: a timestamped directory under /tmp
Schedule: every night at 2 a.m.

Create something worth backing up

Build a small document tree so the backup has real files to copy, including one in a subdirectory.

mkdir -p ~/Documents/notes
echo "Kernel panic on servera, 03:14" > ~/Documents/incident_report.txt
echo "Check disk usage weekly" > ~/Documents/notes/reminders.txt
ls -R ~/Documents

Build and test the backup command

Check what the timestamp looks like, then run the backup by hand. Getting the command right at the prompt first is far easier than debugging it from a crontab.
```
date --iso-8601=minutes
cp -r ~/Documents /tmp/documents_$(date --iso-8601=minutes)
ls -d /tmp/documents_*
```
Why the timestamp matters here cp -r copies into a destination that already exists, which would leave you with documents_.../Documents. Because the timestamp makes a fresh directory every run, the contents land where you expect.
Schedule it one minute from now

A nightly job is hard to test, so schedule it every minute first. Open your crontab and add the entry.
```
crontab -e
```
Press i to enter insert mode and type the line. Use the absolute path, because cron does not expand ~ the way your login shell does.
```
* * * * * cp -r /home/student/Documents /tmp/documents_$(date --iso-8601=minutes)
```
Press Esc to leave insert mode, then type :wq to save. Read the crontab back to confirm it was accepted.
```
crontab -l
```
Avoid % in a crontab command In a crontab entry an unescaped % means a newline, so a timestamp written as date +%F would break the job unless you escape it as \%. --iso-8601 sidesteps the problem entirely.
Confirm it ran

Wait for the next minute to tick over, then read the cron log.
```
sudo less /var/log/cron
```
Press G to jump to the end and q to quit. Look for a matching pair of lines:
```
CROND[11611]: (student) CMD (cp -r /home/student/Documents /tmp/documents_$(date --iso-8601=minutes))
CROND[11609]: (student) CMDEND (cp -r /home/student/Documents /tmp/documents_$(date --iso-8601=minutes))
```
Then look for a second backup directory.
```
ls -d /tmp/documents_*
```
The log shows the command unexpanded cron records the entry exactly as you wrote it, $(date ...) and all. The shell expands it when the job runs, which is why each run lands in its own directory.
Set the real schedule

The command works, so give it the schedule you actually want. Open the crontab again.
```
crontab -e
```
Press C to replace the whole line, and type the nightly version.
```
0 2 * * * cp -r /home/student/Documents /tmp/documents_$(date --iso-8601=minutes)
```
Leave insert mode with Esc, save with :wq, and read it back.
```
crontab -l
```
0 2 * * * is minute 0 of hour 2, every day of the month, every month, every day of the week.
Clean up

Remove the schedule, then the files it produced.
```
crontab -r
crontab -l
rm -rf /tmp/documents_* ~/Documents
```
A harmless warning crontab -r may print /home/student/.cache/crontab: mkdir: No such file or directory. The crontab is removed either way, as crontab -l confirms.

Task

Create something worth backing up

Build and test the backup command

Schedule it one minute from now

Confirm it ran

Set the real schedule

Clean up