What chown does

·         Changes the owner (user) and/or group of files/directories.

·         Only root (or a process with the right capability) can change the owner.

·         The owner of a file can usually change its group to any group they’re a member of.

Check current ownership:

ls -l file

stat -c '%U %G %n' file   # shows owner (%U) and group (%G)

Basic syntax

chown [OPTIONS] OWNER[:GROUP] FILE...

chown [OPTIONS] :GROUP FILE...           # change group only

chown [OPTIONS] --reference=REF FILE...  # copy owner:group from REF

Examples

sudo chown alice file.txt                # set owner to alice

sudo chown alice:devs file.txt           # owner=alice, group=devs

sudo chown :devs file.txt                # only group → devs

sudo chown -R alice:devs project/        # recursive on a tree

sudo chown --reference=/etc/hosts a.txt  # match owner:group of hosts

Options you’ll actually use (GNU chown)

·         -R: recursive (directories and their contents).

·         -v / -c: verbose / report changes only.

·         --from=CUR:GRP: change only if current owner:group matches (safe in scripts).

·         --reference=FILE: copy owner:group from another file.

·         --preserve-root (default): refuse to act on / (safety).

·         Symlink handling (important):

o    -h / --no-dereference: act on the symlink itself.

o    Recursive traversal control:

§  -H: follow symlinks listed on command line.

§  -L: follow all symlinks during recursion.

§  -P (default): do not follow symlinks during recursion.

o    If unsure, stick to the default (-P) to avoid unexpected changes via links.

·         --numeric-ids: interpret OWNER/GROUP as numeric IDs (UID/GID), not names.

Owner vs Group (quick refresher)

·         Every file has one owner (user) and one group.

·         Permissions are applied to owner / group / others (see chmod notes).

·         For team folders, combine group ownership with setgid on the directory so new files inherit the group:

sudo chgrp devs /srv/app

sudo chmod 2775 /srv/app        # 's' on group → inherit group

sudo chown -R :devs /srv/app/*

Common patterns

# Make a whole project owned by a service account:

sudo chown -R www-data:www-data /var/www/myapp

# Give your user ownership of a copied dataset:

sudo chown -R $USER:$USER ~/datasets

# Only switch group (you are a member of 'devs'):

chown :devs script.sh   # (no sudo needed if you own the file)

Typical errors & fixes

·         “Operation not permitted”: you’re not root and trying to change owner; use sudo.

·         “invalid group” / “invalid user”: the name doesn’t exist; check /etc/passwd & /etc/group or getent passwd/group.

·         On WSL/Windows drives (/mnt/c): ownership may not behave as expected (NTFS). Mount with metadata support or work inside your Linux home (~) for proper UNIX ownership.

Good scripting habits

# Change only if currently owned by 'root:root'

sudo chown --from=root:root -R alice:devs /data/shared

# Copy ownership from a template file (idempotent & readable)

sudo chown --reference=/var/www . -R

Mini-lab (10–15 min)

mkdir -p ~/lab/chown && cd ~/lab/chown

echo "data" > a.txt

ls -l a.txt

# make a group folder (simulate with your user + group)

sudo groupadd devs 2>/dev/null || true

sudo chgrp devs a.txt

ls -l a.txt                      # owner stays you; group → devs

# recursive change on a tree

mkdir -p proj/{src,logs}

touch proj/src/app.py proj/logs/app.log

sudo chown -R $USER:devs proj

stat -c '%U %G %n' proj proj/src/app.py proj/logs/app.log

Exam-ready bullets

·         Purpose: change owner and/or group: chown OWNER[:GROUP] file.

·         Root required to change owner; owners can usually change group to one they belong to.

·         Recursive: -R; symlink behavior: default don’t follow (-P), use -h, -H, -L intentionally.

·         Reference & conditional: --reference=FILE, --from=OLD:OLDG.

·         Numeric IDs: --numeric-ids to force UID/GID.

·         Use with team dirs + setgid (chmod 2775 dir) so new files inherit the group.