Essential Unix Commands Every PostgreSQL DBA Should Know

1. Run programs in the background

Use nohup to detach a script from the terminal and keep it running after logout: nohup /root/generate_report.sh & Alternatively, press Ctrl+Z to suspend a running process and then type bg to resume it in the background. Verify with:

ps -ef | grep report

2. Inspect and manage the mail queue (Postfix)

mailq -i

– display the mail queue. postcat -vq <message-id> – view the full content of a specific message. postqueue -f – force immediate processing of the queue. postfix flush – attempt to send all queued mail right away. postsuper -d ALL – delete all queued messages (only those pending retry).

3. Send email with attachments

Using mutt:

echo "<This is the message body>" | mutt -a <file_name> -s "Notification_Subject" <email_address>

Using mailx:

echo "From 'hostname' server the attachment" | mailx -s "mailx test mail" -a /proc/meminfo [email protected]

4. Find files containing a specific string

find . -type f -exec grep -l "word" {} +

– list only file names that contain the word. find / -type f -exec grep -H 'text-to-find-here' {} \; – print matching file names with the matching line.

Example on PostgreSQL logs:

find . -type f -exec grep -H 'max' {} \;

5. Locate and delete files older than X days

find /path/to/files* -mtime +5 -exec rm {} \;

find /var/arhive_backup -mtime +5 -exec ls -l {} \;

find /backup/logs/ -name 'daily_backup*' -mtime +21 -exec rm -f {} \;

6. Compress and extract archives

Step‑by‑step packing:

tar -cf packed_files.tar file1 file2 ...

gzip packed_files.tar

One‑liner packing: tar -cf - file1 file2 ... | gzip -c > packed_files.tar.gz Create a tar from a directory: tar -cvf packed_files.tar dir_to_pack Extract a tar archive: tar -xvf file_to_unpack.tar Two‑step extraction:

gunzip packed_files.tar.gz

tar -xf packed_files.tar

One‑command extraction: gunzip -c packed_files.tar.gz | tar -xf - List contents of a tar file: tar -tvf file_to_list.tar Replace gzip with bzip2 / bunzip2 if desired.

7. Compare two files

Basic diff: diff README.txt README2.txt Ignore whitespace: diff -t file1 file2 Ignore case: diff -i file1 file2 Side‑by‑side view:

diff -y file1 file2 -W 120

8. Synchronize directories remotely with rsync

Copy only differences: rsync -P rsync://rsync.server.com/path/to/file file Rate‑limited local copy: rsync --bwlimit=1000 fromfile tofile Mirror a website (compressed & encrypted):

rsync -az -e ssh --delete ~/public_html/ remote.com:'~/public_html'

Sync current directory with remote and back:

rsync -auz -e ssh remote:/dir/ . && rsync -auz -e ssh . remote:/dir/

9. Move files between timestamps

Find files created between two dates and copy them:

find . -newermt "2015-09-26 00:00:00" ! -newermt "2015-09-26 11:59:59" -exec cp {} /var/lib/pgsql/9.3/cluster2data2/log_edb \;

10. Reboot the system

/sbin/reboot

– immediate reboot. shutdown -r +5 – schedule reboot in 5 minutes (gives users warning). sudo reboot – reboot on Ubuntu/Debian/Fedora with sudo.

It is good practice to broadcast a shutdown message and block new logins during the final minutes.