Exam weight: 2 — LPIC-1 v5, Exam 101
What You Need to Know
- Create hard and symbolic links with
ln. - Distinguish them using
ls -landls -i. - Understand the difference between copying and linking.
- Know hard link limitations: same filesystem only, no links to directories.
Inodes and Links
What is an Inode
An inode is a filesystem data structure storing a file’s attributes: permissions, owner, size, timestamps, and disk block pointers. The filename is not stored in the inode. A filename exists as a directory entry that maps a string to an inode number.
All kernel interaction with a file goes through its inode.
Two Types of Links
Hard link: an additional directory entry pointing to the same inode as the original name. Both names are fully equivalent — there is no way to tell which is the “original.”
Symbolic link (symlink/soft link): a separate file with its own inode whose contents are a path string pointing to the target. When accessed, the kernel follows that path to the target.
Hard Links
Creating a Hard Link
ln TARGET LINK_NAME
ln target.txt /home/carol/Documents/hardlink
Omitting LINK_NAME creates a link with the same name as the target in the current directory.
Link Count and Inode
ls -li
# 3806696 -r--r--r-- 2 carol carol 111702 Jun 7 10:13 hardlink
# 3806696 -r--r--r-- 2 carol carol 111702 Jun 7 10:13 target.txt
- First column — inode number. Same number = same data.
2after permissions — hard link count.- Default count: 1 for regular files, 2 for directories.
- Each new hard link increments the count by 1.
Changes through any name are visible through all others — the data on disk is shared.
Moving and Deleting
Hard links behave like regular files: rm to delete, mv to move/rename. Because the link points to an inode (not a path), moving it does not break the connection.
rm on one name only decrements the counter. Data survives as long as count > 0.
Limitations
- Cannot create a hard link to a directory (prevents directory cycles).
- Cannot create a hard link across filesystem boundaries.
ln /media/user/FlashA/file.txt ~/link
# ln: failed to create hard link ... : Invalid cross-device link
Symbolic Links
Creating a Symbolic Link
ln -s TARGET LINK_NAME
ln -s target.txt /home/carol/Documents/softlink
Unlike hard links: can point to directories and can cross filesystem boundaries.
Identifying in ls Output
ls -lh
# lrwxrwxrwx 1 carol carol 12 Jun 7 10:14 softlink -> target.txt
Indicators: first character l, and -> followed by the target path after the name.
Permissions
A symlink always shows lrwxrwxrwx in ls -l. Real access is determined by the target’s permissions.
Relative vs Absolute Paths
If the target path is relative, it is interpreted relative to the symlink’s location. Moving the symlink to another directory will break it.
# Created in ~/Documents/ — dangerous (relative)
ln -s original.txt softlink
# After mv softlink ../ — broken!
# Fix: always use an absolute path
ln -s /home/carol/Documents/original.txt softlink
Broken Links
When the target is deleted, the symlink remains but points nowhere — a broken (dangling) link. If a file with the same name is later created at the same path, the symlink works again.
Deleting and Moving
Same as regular files: rm link, mv link /new/path.
Copying vs Linking
| Method | Inode | Disk space | Relation to original |
|---|---|---|---|
cp | new | new | independent |
ln (hard) | shared with target | shared | full — same data |
ln -s (symlink) | own, new | a few bytes (path string) | via path to target |
Comparison Table
| Property | Hard link | Symbolic link |
|---|---|---|
| Command | ln T L | ln -s T L |
Type in ls -l | - (like a file) | l |
| Own inode | no, shared | yes |
| Increments link count | yes | no |
| Cross filesystem | no | yes |
| Link to directory | no | yes |
| When target deleted | data survives (count ≥ 1) | link breaks |
Size in ls -l | same as target | length of path string |
Uses in System Administration
- Version switching:
/usr/bin/python→python3.11. Retarget the link to switch interpreters without editing scripts. - nginx
sites-enabled: config files are symlinks tosites-available/. - Incremental backups (
rsync --link-dest): unchanged files are hard links to the previous snapshot — space-efficient while each snapshot looks complete. - Convenience access: symlink in
~pointing to/var/log/myapp/.
Quick Reference
# Hard link
ln target.txt hardlink
# Symbolic link
ln -s target.txt softlink
# Symbolic link with absolute path (safe)
ln -s /home/user/file.txt /home/user/links/file
# Overwrite an existing link
ln -sf newtarget.txt softlink
# Show inode number and link count
ls -li
# Show inode number only
ls -i
# Delete any link
rm link
# Move a link
mv link /new/path
Exam Questions
- What happens when the target of a hard link is deleted? → Data remains accessible through the link; count drops to 1, not 0.
- What happens when the target of a symlink is deleted? → The symlink becomes broken:
No such file or directory. - Can you create a hard link to a directory? → No, only a symbolic link.
- Can you create a hard link across filesystem boundaries? → No:
Invalid cross-device link. Use a symlink instead. - Which
lsflag shows the inode number? →-i. - What permissions does a symlink show in
ls -l? → Alwayslrwxrwxrwx. Real access is from the target. - How does a copy differ from a hard link? → A copy has its own inode and disk space; a hard link shares the inode and data with the target.
- How to create
c.txtwith the same inode asa.txt? →ln a.txt c.txt. - Does a symlink increase the target’s link count? → No.
- Why does a relative symlink break when moved? → The target path is resolved relative to the symlink’s location; in the new directory, that relative path leads nowhere.
Exercises
Exercise 1 — Enable the sticky bit with chmod
Which symbolic-mode chmod option enables the sticky bit on a directory?
Answer
chmod +t /path/to/dir
# or explicitly for others:
chmod o+t /path/to/dir
The sticky bit symbol is t. To enable it, use +t.
Exercise 2 — Create a symbolic link
The file document.txt is in /home/carol/Documents. Create a symbolic link named text.txt in the current directory pointing to it.
Answer
ln -s /home/carol/Documents/document.txt text.txt
The -s flag creates a symbolic link. Using the full path prevents the link from breaking if it is ever moved.
Exercise 3 — Hard link vs copy
Explain the difference between a hard link to a file and a copy of that file.
Answer
A hard link is another name for the same file. Link and original share one inode and one set of disk blocks. Changes through any name are visible through all others.
A copy is a fully independent entity with its own inode and its own disk space. Changes to the copy do not affect the original.
Exercise 4 — Deleting the target of a symlink
Given:
touch recipes.txt
ln recipes.txt receitas.txt
ln -s receitas.txt rezepte.txt
What happens to rezepte.txt after rm receitas.txt?
Answer
rezepte.txt becomes a broken link. Symlinks point to names, not inodes. The name receitas.txt no longer exists, so the symlink leads nowhere.
The data itself survives on disk and is accessible via recipes.txt (a hard link with the same inode), but the symlink has no knowledge of that.
Exercise 5 — Hard link to a flash drive
A USB drive is mounted at /media/youruser/FlashA. You run:
ln /media/youruser/FlashA/esquema.pdf ~/schematics.pdf
What happens? Why?
Answer
The command fails with Invalid cross-device link. Hard links cannot span different devices or filesystems — an inode is only meaningful within its own filesystem.
Fix — use a symlink:
ln -s /media/youruser/FlashA/esquema.pdf ~/schematics.pdf
Exercise 6 — Analysing ls output for link count
-rw-rw-r-- 1 carol carol 2,8M jun 17 15:45 compressed.zip
-rw-r--r-- 4 carol carol 77K jun 17 17:25 document.txt
-rw-rw-r-- 1 carol carol 216K jun 17 17:25 image.png
-rw-r--r-- 4 carol carol 77K jun 17 17:25 text.txt
How many links point to document.txt? Are they hard or symbolic? Which ls flag shows inode numbers?
Answer
Link count is 4. Starting count is 1 (the name itself), so 3 additional hard links were created.
They are hard links — symlinks do not increase the target’s link count.
Flag -i:
ls -lahi
# 5388833 -rw-r--r-- 4 document.txt
# 5388833 -rw-r--r-- 4 text.txt
document.txt and text.txt share inode 5388833 → text.txt is one of those hard links.
Exercise 7 — Moving a relative symlink
Directory structure:
~/Documents/
├── clients.txt ("John, Michael, Bob")
└── somedir/
├── clients.txt ("Bill, Luke, Karl")
└── partners.txt -> clients.txt (relative symlink)
After mv ~/Documents/somedir/partners.txt ~/Documents/, what does less ~/Documents/partners.txt show?
Answer
The link works, but shows ~/Documents/clients.txt — John, Michael, Bob — not the intended file.
partners.txt stores clients.txt as a relative path, resolved from its current location. After moving from somedir/ to Documents/, the link looks for clients.txt next to itself — and finds Documents/clients.txt instead.
Fix: always use an absolute path when creating symlinks:
ln -s /home/carol/Documents/somedir/clients.txt partners.txt
Exercise 8 — Symlink permissions
-rw-r--r-- 1 carol carol 19 Jun 24 11:12 clients.txt
lrwxrwxrwx 1 carol carol 11 Jun 24 11:13 partners.txt -> clients.txt
What are the actual access permissions for partners.txt?
Answer
rw-r--r-- — the target’s permissions (clients.txt).
A symlink always shows lrwxrwxrwx in ls -l, but those are its own metadata. Access through the link is governed by the target’s permissions.
LPIC-1 Study Notes | Topic 104: Devices, Linux Filesystems, Filesystem Hierarchy Standard