q29-links-and-file-attributes

Énoncé§

Solve this question on: terminal

1. Create a hard link /opt/course/29/hard-passwd pointing to /etc/passwd.
2. Create a symbolic link /opt/course/29/soft-passwd pointing to /etc/passwd.
3. Make /etc/resolv.conf immutable so even root cannot edit it without removing the attribute.
4. Write the inode number of /etc/hostname into /opt/course/29/inode.

Solution§

Step 1 — Hard link§

sudo ln /etc/passwd /opt/course/29/hard-passwd
ls -li /etc/passwd /opt/course/29/hard-passwd
# both entries share the same inode and link count goes up

Hard link properties:

• Points to the same inode as the original.
• Cannot cross filesystems.
• Cannot point to a directory (kernel protection).
• The file is only deleted when all hard links are removed.

Step 2 — Symbolic link§

ln -s /etc/passwd /opt/course/29/soft-passwd
ls -l /opt/course/29/soft-passwd
# lrwxrwxrwx ... soft-passwd -> /etc/passwd

Symbolic link properties:

• Stores a path (not an inode reference).
• Can cross filesystems and link directories.
• Broken if the target moves or is deleted (ls -l shows red).

Useful flags:

• ln -sf target name — force replace existing link
• ln -sr target name — make the symlink relative
• readlink -f link — resolve to absolute path
• stat file — show inode, links, size, timestamps

Step 3 — File attributes with chattr§

sudo chattr +i /etc/resolv.conf       # immutable
lsattr /etc/resolv.conf
# ----i---------e----- /etc/resolv.conf
sudo chattr -i /etc/resolv.conf       # remove

Common attributes:

Step 4 — Inode number§

stat -c %i /etc/hostname > /opt/course/29/inode
# or:
ls -i /etc/hostname | awk '{print $1}' > /opt/course/29/inode

Extended attributes (xattr)§

Separate from chattr; used by SELinux, ACLs, custom metadata:

getfattr -d -m '.*' file              # show all
setfattr -n user.note -v "hello" file
setfattr -x user.note file