This article compiles essential Linux commands for system administration, covering file operations, text processing, process management, and other core tasks. It serves as a quick reference for daily operations.
File and Directory Operations
Commands for navigating, viewing, and managing files and directories.
cd (Change Directory)
Changes the current working directory.
cd /home # Enter '/home' directory
cd .. # Go up one directory level
cd ../.. # Go up two directory levels
cd # Go to the current user's home directory
cd ~user1 # Go to user1's home directory
cd - # Return to the previous directorypwd (Print Working Directory)
Displays the absolute path of the current directory.
$ pwd
/home/userls (List Directory Contents)
Lists files and subdirectories.
ls # List contents of current directory
ls -l # Long listing (permissions, owner, size, etc.)
ls -a # List all files, including hidden ones (starting with .)
ls -R # Recursively list subdirectory contents
ls [0-9]* # List files/directories whose names start with a digitcp (Copy)
Copies files or directories.
cp source_file dest_file # Copy a file
cp -r source_dir dest_dir # Recursively copy a directory (common)
cp -a source dest # Archive copy, preserving all attributes
cp -i source dest # Prompt before overwriting
cp -u source dest # Copy only if source is newermv (Move/Rename)
Moves or renames files/directories.
mv old_name new_name # Rename a file or directory
mv file /target/dir/ # Move a file to a target directory
mv -i source dest # Prompt before overwriting
mv -u source dest # Move only if source is newerrm (Remove)
Deletes files or directories. Use with caution, especially recursive deletion.
rm file # Delete a file
rm -r directory # Recursively delete a directory (dangerous)
rm -f file # Force delete, ignore missing files, no prompt
rm -i file # Interactive delete, confirm before removalViewing File Content
Commands for viewing and browsing text files.
cat (Concatenate and Display)
Outputs entire file content to standard output.
cat file.txt # Display entire file content
cat -n file.txt # Display with line numbers
tac file.txt # Display content in reverse (last line first)more / less (Paged Viewing)
View long files page by page. less is more powerful, supporting forward/backward navigation.
more long_file.log # View with forward-only paging
less long_file.log # View with full navigation and searchhead / tail (View Beginning/End)
View the beginning or end of a file.
head -n 20 file.log # View first 20 lines
tail -n 50 file.log # View last 50 lines
tail -f /var/log/app.log # Follow (monitor) new content in real-time (common)
tail -n +100 file.log # Display from line 100 to endCombination example: View lines 1000 to 3000 of a file.
cat filename | head -n 3000 | tail -n +1000
# Or
sed -n '1000,3000p' filenameFile Search
Find files in the filesystem.
find (Find Files)
Powerful real-time file search tool.
find / -name "myfile.txt" # Search from root by name
find /home -user username # Find files owned by a user
find /var/log -type f -mtime -7 # Find regular files modified within 7 days in /var/log
find /tmp -size +100M # Find files larger than 100MB in /tmp
find . -name "*.log" -exec rm {} ; # Find and delete all .log files (dangerous)which / whereis (Find Commands)
Locate executable commands.
which ls # Show full path of ls command
whereis python # Show binary, source, and manual page locationsFile Permissions and Ownership
Manage access permissions for files and directories.
chmod (Change Mode)
Modify permissions using symbolic (u/g/o/a, +/-, r/w/x) or numeric (octal) modes.
chmod u+x script.sh # Add execute permission for owner
chmod 755 directory # Set directory permissions to rwxr-xr-x
chmod go-w file.txt # Remove write permission for group and otherschown / chgrp (Change Owner/Group)
Change file owner and group.
chown user:group file # Change both owner and group
chown -R user:group /project # Recursively change owner/group for directory
chgrp developers file # Change file group onlyText Processing
Filter, transform, and analyze text content.
grep (Global Regular Expression Print)
Search for lines matching a pattern.
grep "error" /var/log/syslog # Search for lines containing "error"
grep -r "TODO" ./src # Recursively search all files in current directory
grep -v "^#" config.conf # Show all non-comment lines (not starting with #)
grep -E "[0-9]{3}-[0-9]{4}" file # Use extended regex to match phone number patternsed (Stream Editor)
Filter and transform text.
sed 's/old/new/g' file # Replace all 'old' with 'new' in file
sed '/^$/d' file # Delete all empty lines in file
sed -n '5,10p' file # Print only lines 5 to 10 of filesort / uniq (Sort and Deduplicate)
Sort text lines and remove duplicates.
sort file.txt # Sort lines of file
sort -u file.txt # Sort and remove duplicates
uniq sorted_file.txt # Report or omit repeated lines (usually after sorting)
uniq -c sorted_file.txt # Count occurrences of duplicate linespaste / comm (Merge and Compare)
paste file1 file2 # Merge two files side-by-side (column merge)
comm -12 file1 file2 # Output intersection of two sorted files
comm -3 file1 file2 # Output lines unique to each file (symmetric difference)Archiving and Compression
Archive and compress files and directories.
tar (Tape Archive)
Create archive files, optionally with gzip/bzip2 compression.
# Create compressed archive (common combinations)
tar -czvf archive.tar.gz /path/to/dir # Compress with gzip
# Extract archive
tar -xzvf archive.tar.gz -C /target/dir # Extract to target directory
# List archive contents
tar -tzvf archive.tar.gzgzip / bzip2 / xz (Compression Tools)
gzip file # Compress file, producing file.gz
gunzip file.gz # Decompress .gz file
bzip2 file # Compress with bzip2, producing file.bz2
xz file # Compress with xz (often higher compression ratio)zip / unzip
zip -r archive.zip dir/ # Recursively compress directory
unzip archive.zip # Extract zip file
unzip -l archive.zip # List contents of zip fileSystem Shutdown and Reboot
shutdown -h now # Shut down immediately
shutdown -r +10 "System rebooting in 10 minutes" # Reboot in 10 minutes with message
shutdown -c # Cancel scheduled shutdown/reboot
reboot # Reboot immediately
poweroff # Power off immediately (some systems)
logout # Log out current session
time command # Measure command execution timeProcess Management
View and manage system processes.
ps (Process Status)
ps aux # View detailed info for all processes (common)
ps -ef # List all processes in full format
ps aux | grep nginx # Find processes related to nginxtop / htop (Dynamic Process View)
Real-time display of system processes and resource usage. htop is an enhanced, more interactive version of top.
top # Start dynamic process viewer
htop # Feature-rich process viewer (may require installation)kill / killall / pkill (Terminate Processes)
Send signals to processes. Default is TERM (15) to request termination.
kill 1234 # Request termination of process with PID 1234
kill -9 1234 # Force kill process (SIGKILL, cannot be caught/ignored)
killall -9 process_name # Force kill all processes named process_name
pkill -f "python script.py" # Kill processes by matching full command linejps (Java Process Status)
View Java processes (requires JDK).
jps # List Java processes and their PIDs
jps -l # Output full package name of main classnetstat / ss (Network Connections and Ports)
View network connections, routing tables, interface statistics. ss is a modern, faster replacement for netstat.
netstat -tunlp | grep :80 # Find process listening on port 80
ss -tlnp # List all listening TCP ports and processes (faster)Mastering these fundamental commands will significantly improve efficiency in Linux administration. Practice them in real scenarios and use man [command] or [command] --help to consult detailed manuals.