Linux FS: navigation, search, files for developers

Linux Basics: Filesystem Structure, Navigation, and File Management

The root directory / sits at the top of the hierarchy, where all other partitions are mounted. Key directories define their purposes: /etc for configurations, /var for dynamic data, /proc and /sys as virtual interfaces to the kernel.

/
├── etc        # system and app configurations
├── var        # variable data: logs, cache, queues
├── proc       # kernel and process status
├── sys        # devices and drivers
├── tmp        # temporary files
├── home       # user home directories
├── root       # root user's home
├── dev        # device files
├── usr        # programs and libraries
├── bin        # essential utilities (symlink to /usr/bin)
├── sbin       # admin commands (symlink to /usr/sbin)
├── opt        # third-party software
├── run        # runtime process data
├── mnt        # manual mount points
└── boot       # bootloader and kernel files

/etc: Centralized Configurations

Holds config files for services, network settings, and users. Key files include /etc/passwd for user accounts, /etc/fstab for mount points, /etc/hosts for local hostname resolution, and /etc/ssh/sshd_config for SSH settings.

/var: Dynamic Data

Stores changing files like logs in /var/log, mail in /var/mail, print queues in /var/spool, and web server content in /var/www. It's your first stop for troubleshooting.

Virtual Filesystems: /proc and /sys

/proc provides real-time data on processes and the kernel: /proc/cpuinfo for CPU details, /proc/meminfo for memory stats, /proc/1/ for the init process. /sys offers an interface to devices, letting you tweak driver and hardware parameters on the fly.

User Directories and Devices

/home/username houses personal files and configs (like .config and .ssh). /root is isolated for the root user. /dev represents hardware: /dev/sda for a disk, /dev/null to discard output, /dev/random for entropy.

Navigation: ls, cd, pwd

ls lists directory contents with flags for more details.

• ls -l: permissions, owner, size, date.
• ls -a: hidden files.
• ls -lh: human-readable sizes (KB/MB/GB).
• ls -lt: sort by time.
• ls -R: recursive listing.

cd changes directories:

• cd /etc: absolute path.
• cd ..: go up one level.
• cd ~: home directory.
• cd -: previous directory.

pwd prints the current path: pwd -P resolves symlinks.

Finding Files: find and locate

find searches recursively based on criteria.

Examples:

• find . -name "*.log": log files.
• find /var -type f: files only.
• find / -size +100M: files over 100MB.
• find /var/log -mtime -1: logs modified in the last day.
• find /tmp -name "*.tmp" -delete: clean up temp files.

locate uses a database for speed:

• locate passwd.
• sudo updatedb to refresh the index.

On Ubuntu 22.04+, use plocate for better performance.

tree visualizes directory structures: tree -L 2 -a -I "node_modules".

File Management: cp, mv, rm

cp copies:

• cp file.txt /tmp/.
• cp -r dir1/ /backup/.
• cp -p preserves metadata.
• cp -u updates only newer files.

mv moves or renames: mv old.txt new.txt, mv *.log /archive/.

rm deletes without a trash bin:

• rm -r dir/.
• rm -rf / — extremely dangerous, never run.
• rm -i prompts for confirmation.

Creating and Linking: mkdir, touch, ln

mkdir -p /path/to/dir creates nested directories.

touch file.txt creates an empty file or updates timestamps: touch -t 202501011200 file.txt.

ln creates links:

• ln file.txt hardlink.txt — hard link (shares inode).
• ln -s file.txt symlink.txt — symbolic link (points to path).

Hard links don't work across filesystems; symlinks are flexible but break if the original is deleted.

Key Takeaways:

• /proc and /sys are in-memory, not on disk—purely for kernel runtime data.
• find is versatile; locate is fast with a maintained index.
• rm -rf demands caution—no recycle bin safety net.
• mkdir -p and cd - are scripting essentials.
• Hard vs. symbolic links: pick based on needs (shared data vs. path reference).

— Editorial Team