CTF TOPIC · 6 FLAGS · 20 MIN

Linux and the terminal

Hidden files, grep, find, permissions, pipes and strings on the command line.

Most CTF work happens in a Linux shell. ls -la shows hidden dotfiles; grep -r searches many files for a pattern; find searches by name, size or owner; permission strings (rwx for owner/group/others) decide who can read a file; pipes (|) chain small tools together; and strings pulls readable text out of a binary. These few commands solve a surprising number of challenges.

A first example

ls -la ; grep -r 'flag{' . ; find / -size 33c ; cat file | sort | uniq -c | sort -rn

First moves

1. ls -la in every new directory
2. grep -r 'flag{' from the top of what you can read
3. find by name, size, owner or recent change
4. Read permission strings before trying to open files
5. Pipe tools together: sort | uniq -c | sort -rn

The challenges

• Dotfiles · Easy · 20 XP
• Grep the haystack · Easy · 20 XP
• Find by size · Easy · 20 XP
• Read the permissions · Medium · 30 XP
• Pipes and sort · Easy · 20 XP
• Strings in a binary · Medium · 30 XP