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9 Linux Tricks

9 Linux Tricks

Anyone can navigate a file system. But a true System Engineer knows how to manipulate process memory, recover lost sessions, and create disk space out of thin air when the server hits 100% utilization at 3 AM.

These are not just commands; they are survival tools. Here are 9 advanced Linux tricks to elevate you from a user to a master :)

Table of Contents

  1. Ghost Hunting: Finding deleted files consuming disk space (lsof)
  2. Time Travel: Moving a running process into a screen (reptyr)
  3. The X-Ray Machine: Debugging processes without logs (strace)
  4. Config Espionage: Reading a running process’s environment (/proc)
  5. The Panic Button: Instant disk space for Root (tune2fs)
  6. SSH Turbo Mode: Connection multiplexing (ControlMaster)
  7. The Quick Fix: correcting typos instantly (^old^new)
  8. Modern Network Analysis: netstat is dead, long live ss
  9. Muscle Memory: sudo !! and !$

1. Ghost Hunting: lsof +L1

Scenario: df -h says disk usage is 100%, but you just deleted gigabytes of log files. Reason: If a process (like Apache or Postgres) is still writing to a file you deleted, the OS doesn't free the space (inode). It becomes a "zombie" file.

The Fix:

lsof +L1
# Look for files marked as (deleted) but still held by a PID.
# You must reload/restart that specific PID to free the space.

2. Time Travel: reptyr

Scenario: You started a long script, it’s been running for 4 hours, but you forgot to start a screen or tmux session. You need to disconnect, but closing the terminal will kill the script.

The Fix: Use reptyr to "steal" the process and reparent it to a new screen.

# 1. Background the process: Ctrl+Z, then type 'bg'
# 2. Disown it from current shell: 'disown <PID>'
# 3. Open a new screen/tmux and pull it in:
reptyr <PID>

3. The X-Ray Machine: strace

Scenario: A process is hanging. No logs. No CPU usage. Is it waiting for network? Is it permission denied? The Fix: Don’t guess. Watch the system calls in real-time.

strace -p <PID>
# You will see exactly what the kernel is doing: 
# open(), connect(), read()... 
# This is the ultimate debugging weapon.

4. Config Espionage: /proc Filesystem

Scenario: A developer claims, “It works on my machine,” but the production service fails. You suspect it picked up the wrong DB password or API key from the environment. The Fix: Read the memory of the running process directly.

cat /proc/<PID>/environ | tr '\0' '\n'
# This dumps every environment variable the process was started with.
# No more guessing.

5. The Panic Button: tune2fs

Scenario: Production is down. Disk is 100% full. You can’t even tab-complete commands because there is zero space for temp files. The Fix: Linux reserves 5% of blocks for the root user by default. In an emergency, you can set this to 0% to instantly gain GBs of space.

tune2fs -m 0 /dev/sdX
# Warning: Set it back to 5% once you clean up!

6. SSH Turbo Mode: ControlMaster

Scenario: Running Ansible or opening multiple tabs to the same server is slow because of the SSH handshake. The Fix: Enable connection multiplexing. The first connection authenticates; subsequent connections slide through the existing tunnel instantly.

# In your ~/.ssh/config:
Host *
    ControlMaster auto
    ControlPath ~/.ssh/sockets/%r@%h-%p
    ControlPersist 600

7. The Quick Fix: ^old^new

Scenario: You typed a long command with a typo. systemctl restart nginxx The Fix: Don't hit the up arrow and scroll back.

^nginxx^nginx
# Bash automatically runs: systemctl restart nginx

8. Modern Network Analysis: ss

Scenario: You are still using netstat. The Fix: netstat is deprecated, slow, and truncates output. ss (Socket Statistics) talks directly to the kernel and is blazing fast.

ss -tulpn
# -t: TCP, -u: UDP, -l: Listening, -p: Process, -n: Numeric
# See everything listening on your server in milliseconds.

9. Muscle Memory: sudo !! and !$

  • sudo !!: You typed a command but forgot sudo.
  • Action: Type sudo !! (runs the last command as root).
  • !$: You created a directory and now want to go into it.
mkdir -p /var/www/html/project/v2 cd !$  
# '!$' expands to the last argument of the previous command

Conclusion

These tricks aren’t just for showing off; they are for saving the day when standard tools fail. Master these, and the terminal becomes an extension of your mind, not just a black screen.

Which of these “dark arts” do you use the most? Let me know in the comments.