Essential Linux Command-Line Tricks: Checksums, File Search, Process Management & More

1. View File Checksums

When copying or transferring files, verifying integrity is crucial; you can compare MD5, CRC, or generic sum values. Common commands are:

md5sum file_name
cksum file_name
sum algorithm_option file_name

Example with test.txt:

MD5: md5sum test.txt CRC: cksum test.txt Sum with system V algorithm: sum -r test.txt Sum with BSD algorithm: sum -s test.txt System V is the default when no option is given.

2. Locate Files

(1) locate

locate

searches a pre‑built database ( /var/lib/slocate) and is usually faster than find. Install it if missing (e.g.,

apt-get update
apt-get install mlocate

on Ubuntu) and use:

locate file_name

(2) find

find

can filter by name, type, owner, size, etc. Basic syntax: find path -option file_name Example to locate stdio.h:

find / -name stdio.h

3. Command‑Line Editing Shortcuts

To quickly clear a long, mistyped command, press Ctrl+U . Additional useful shortcuts:

Ctrl+K : delete from cursor to end of line.

Ctrl+A : move cursor to line start.

Ctrl+E : move cursor to line end.

4. View a Process PID

pidof process_name

5. Inspect Specific Process Activity

Use top with the PID to monitor a single process: top -p `pidof kcalc` Multiple processes can be listed by repeating -p `pidof …` options.

6. Terminate Processes

(1) kill

Find the PID with pidof then run:

kill -9 process_pid

(2) killall

Terminate by name directly:

killall process_name

7. Save Terminal Output to a File

(1) tee

Redirect output while still displaying it:

executable_file | tee log_file

(2) script

Record an entire session:

Start recording: script log.txt End recording: type

exit

(3) Terminal tools with built‑in logging

Some terminals (e.g., Terminator) provide a UI option to save logs.

8. View Dynamic Library Dependencies

ldd executable_file

9. Inspect ELF File Header

Use readelf -h to display architecture and other metadata, or file for a quick summary.

readelf -h elf_file

10. Text File Viewing Utilities

(1) cat

Displays file contents; -n adds line numbers.

cat -n /etc/profile

(2) tac

Shows file from bottom to top.

(3) more

Paginated view with progress percentage.

more file

(4) less

More flexible pagination; supports forward and backward navigation.

less file

(5) head

Shows the first n lines.

head -n 20 /etc/profile

(6) tail

Shows the last n lines.

tail -n 20 /etc/profile

(7) nl

Similar to cat -n, prints line numbers.

nl file

11. Set LD_LIBRARY_PATH

The environment variable tells the linker where to search for shared libraries. Append the current directory like this: export LD_LIBRARY_PATH=./:$LD_LIBRARY_PATH These concise tips can streamline everyday Linux system work.