What is Symbolic Link? | DevOps Dictionary

What Is a Symbolic Link in Simple Terms

A symbolic link is a shortcut — like a Windows shortcut or a macOS alias. It is a file that says "the thing you are looking for is actually over there." When you open the shortcut, the system transparently redirects you to the real thing.

The classic real-world use: a deployment system keeps the current version of an application at /opt/app/current. Instead of updating every config file when a new version is deployed, current is a symlink that gets updated to point to the new version directory.

How It Works

A symlink has its own inode. The data stored in its data block is just the target path as text — not the actual file content.

◈ DIAGRAM

Symlink inode 9876
+---------------------------+
| Type: symlink (l)         |
| Contents: /opt/app/v2.0/  |
+---------------------------+
         |
         | kernel follows path
         v
/opt/app/v2.0/
+---------------------------+
| index.html                |
| config.yaml               |
| bin/                      |
+---------------------------+

Hard link vs symbolic link comparison:

◈ DIAGRAM

Hard Link                     Symbolic Link
+-----------------------------++-----------------------------+
| Same inode as target        || Own inode                   |
| Link count increments       || Link count unchanged        |
| Cannot cross filesystems    || Can cross filesystems       |
| Cannot point to directory   || Can point to directory      |
| Works if target deleted     || Breaks if target deleted    |
| ls shows as regular file    || ls shows as l, shows target |
+-----------------------------++-----------------------------+

Practical Commands

Bash

## Create a symbolic link
ln -s /opt/app/v2.0 /opt/app/current
## Now /opt/app/current -> /opt/app/v2.0
 
## Create symlink to a file
ln -s /etc/nginx/sites-available/mysite /etc/nginx/sites-enabled/mysite
 
## View symlinks
ls -la /opt/app/current
## lrwxrwxrwx 1 root root 14 Jan 15 /opt/app/current -> /opt/app/v2.0
 
## Read target path
readlink /opt/app/current
## /opt/app/v2.0
 
## Resolve full absolute path (follows all symlinks)
readlink -f /opt/app/current
## /opt/app/v2.0
 
## Update symlink to new version (atomic)
ln -sf /opt/app/v3.0 /opt/app/current
## -f forces overwrite. This is atomic -- no window where link is broken
 
## Find all symlinks in a directory
find /etc -type l
 
## Find broken symlinks (target does not exist)
find /etc -xtype l
 
## Remove a symlink (NOT the target)
rm /opt/app/current
## or
unlink /opt/app/current
 
## Check if a path is a symlink in a script
if [ -L /opt/app/current ]; then
  echo "It is a symlink"
fi

Production deployment pattern:

Bash

## Deploy new version without downtime
SEMVER="v3.0.1"
 
## Step 1: Extract new version
tar xzf app-${SEMVER}.tar.gz -C /opt/app/
 
## Step 2: Run database migrations, build steps, etc.
/opt/app/${SEMVER}/scripts/migrate.sh
 
## Step 3: Atomically update the symlink
ln -sf /opt/app/${SEMVER} /opt/app/current
 
## systemd service points to /opt/app/current/bin/server
## Reloading the service now uses the new version
systemctl reload myapp
 
## Rollback: just point current back to previous version
ln -sf /opt/app/v2.9.0 /opt/app/current
systemctl reload myapp

Troubleshooting

Symptom	Command	What to Look For
Symlink not working	`readlink -f symlinkname`	Target path does not exist
Circular symlink	`readlink -f symlinkname`	Output: Too many levels of symbolic links
Broken symlinks in /etc	`find /etc -xtype l`	Lists all broken symlinks
ls shows wrong size for symlink	`stat symlinkname`	Size shown is length of path string, not target

PLACEMENT PRO TIP
**Tip:** `ln -sf` (symbolic, force) is the safest way to update a symlink. It atomically replaces the existing symlink in a single syscall. There is no window where the symlink does not exist, which means services reading through the symlink are never interrupted.

REMEMBER THIS
**Remember:** Deleting a symlink with `rm` removes only the symlink, not the target. This is almost always what you want. To remove the target, you must `rm` the actual file or directory, not the symlink pointing to it.