Essential Linux Command Cheat Sheet for Operations Engineers

1. Search in vi/vim

Use /keyword to search forward; press Enter to jump to the first match, then n to find the next occurrence.

2. Vim undo and binary view

Press Esc then u to undo the last change. To view a file in binary mode, run vim -b mytest.php.

3. Pipe operator

The pipe symbol | passes the output of one command as input to the next. Example: cat install.log | more displays the log page‑by‑page.

4. Find files or directories

Common patterns: find /home -name "hello*" – find files/dirs named starting with hello under /home. find / -name h?m* – match names beginning with h, any character, m, then any suffix. find / -size +1000000k – locate files larger than 1 GB.

5. String replacement in vim

:s/well/good/

– replace first well on the current line. :s/well/good/g – replace all well on the current line. :n,$s/well/good/ – replace first well from line n to the end. :n,$s/well/good/g – replace all occurrences from line n onward. :%s/well/good/ – replace first well in every line. :%s/well/good/g – replace all well in the file.

Use # as an alternate delimiter to avoid escaping slashes, e.g., :s#well/#good/#.

6. Output redirection

ls -l /etc > /home/myback.txt

– overwrite the file with the command output. ls -l /etc >> /home/myback.txt – append the output.

7. Delete multiple lines in vim

Show line numbers with :set nu, then delete a range, e.g., 190,6233d. To clear an entire file, use > log.txt.

8. Jump to a specific line

Enter G for the last line, 1G for the first, or 17G to go to line 17.

9. Copy and paste lines

yy

– yank (copy) the current line; p – paste. 7yy – copy seven lines starting from the current line; p – paste.

10. Check Python version

Run python -V or python --version.

11. grep usage

grep -A n

– show n lines after a match. grep -B n – show n lines before a match. grep -C n – show n lines of context. grep -i pattern – case‑insensitive search.

12. Detailed ll output

ll -ht

lists files sorted by modification time with human‑readable sizes.

13. Find which process uses a file

Use lsof filename.

14. User management

Create a user: useradd redis then set password with passwd redis.

On Ubuntu: useradd openstack -m -s /bin/bash and delete with userdel -r openstack.

View groups in /etc/group and users in /etc/passwd or /etc/shadow.

15. Monitor memory, disk, and CPU

Memory: free -m (‑m for MB, ‑g for GB).

Disk: df -lh (human‑readable).

CPU info: cat /proc/cpuinfo (shows each core); filter with cat /proc/cpuinfo | grep "model name" | head -1 for a single line.

16. Check OS version

Run cat /etc/issue or cat /etc/redhat-release. For low‑level details, cat /proc/version.

17. Disk usage of a directory

du -h node

(run inside the target directory) or du -sh * from / to list sizes of all entries.

18. Inspect memory usage of Java processes

jstat -gc pid

– garbage‑collection stats. jmap -heap pid – heap layout. jstat -gcutil pid 1000 – GC utilization every second.

19. Change ownership recursively

chown -R solr:solr /home/solr/lib

changes user and group for the directory and its contents.

20. Check port connection counts

netstat -nlap | grep -i est | grep -i 6379 | awk '{print $4}'

netstat -nlap | grep -i est | grep -i 1121 | wc -l

Common netstat flags: -a (all), -t (TCP), -u (UDP), -n (numeric), -l (listening), -p (program name), -r (routing), -e (extra info), -s (statistics), -c (continuous).

21. Synchronize server time

Run ntpdate pool.ntp.org and schedule with a cron entry like 1 */2 * * * ntpdate pool.ntp.org.

22. Restrict SSH login

Edit /etc/sysconfig/sshd_config (or /etc/ssh/sshd_config) to add AllowUsers solr, then reload with service sshd reload.

23. Common JDK environment variables

JAVA_HOME=/usr/java/jdk1.7.0_55

CLASSPATH=.:$JAVA_HOME/lib/tools.jar

PATH=$JAVA_HOME/bin:$PATH

Export them with

export JAVA_HOME CLASSPATH PATH

24. Check Redis and Tomcat versions

Redis: redis-cli info | grep 'redis_version' Tomcat: run ./version.sh or sh version.sh inside the bin directory.

25. Verify if firewall blocks port 80

Execute iptables -vnL | grep ":80 "; output indicates the rule is present.