systemd-tmpfiles.d

systemd-tmpfiles manages the creation, deletion, and cleanup of volatile runtime directories like /tmp, /run, /var/run, /var/tmp. It runs early in boot to set up the runtime filesystem hierarchy and periodically to clean up old files.

Why It Exists

/tmp    — shared temp space (user can write anything)
          Needs to be cleared on reboot, cleaned periodically

/run    — runtime data (pid files, sockets, lock files)
          Must exist before services start

/var/run — symlinked to /run on modern systems
           Same purpose as /run

Before tmpfiles, /tmp was a mess of stale files. Services had to create their directories at startup (race condition prone). tmpfiles.d provides a declarative way.

Configuration Files

# Config locations (processed in order):
/etc/tmpfiles.d/*.conf      # admin overrides (highest priority)
/run/tmpfiles.d/*.conf      # runtime-generated configs
/lib/tmpfiles.d/*.conf      # vendor defaults (lowest priority)

Syntax

Type  Path                  Mode UID    GID    Age    Argument
d     /run/myapp            0755 root   root   -      -
f     /run/myapp/pid        0644 root   root   -      1234
D     /tmp/myapp-cache      0755 darshan darshan 1d   -
L     /run/app.sock         -    -      -      -      /dev/null
C     /run/config           -    -      -      -      /etc/default/config

Types

Type	Action
d	Create directory if it doesn’t exist
D	Create directory, delete on boot (clean start)
f	Create regular file
F	Create regular file, truncate if exists
w	Write the Argument string to the file
L	Create symlink
c	Create character device
b	Create block device
p	Create named pipe (FIFO)
C	Copy directory tree recursively

Fields

d  /run/example  0755  root  root  -
│  │              │     │     │    │
│  │              │     │     │    └─ Age: cleanup if not accessed for N days
│  │              │     │     └─ GID
│  │              │     └─ UID
│  │              └─ Mode (octal)
│  └─ Path
└─ Type

Common Examples

/tmp cleanup (default config)

cat /lib/tmpfiles.d/tmp.conf
# See the system defaults for /tmp

Create runtime directory for your app

# /etc/tmpfiles.d/myapp.conf
# Create /run/myapp on boot, clean if unused for 30 days
d  /run/myapp  0755  myapp  myapp  30d

Pre-create PID file

# /etc/tmpfiles.d/myapp.conf
# Create /run/myapp.pid with content "1234"
f  /run/myapp.pid  0644  root  root  -  1234

Create symlink

# /etc/tmpfiles.d/socket.conf
# Link /run/app.sock → /dev/null (useful for nulling a socket)
L  /run/app.sock  -  -  -  -  /dev/null

Managing tmpfiles

# Run manually (creates/cleans now)
systemd-tmpfiles --create
systemd-tmpfiles --clean
systemd-tmpfiles --remove    # DELETE everything matching configs!
 
# Full cycle (create dirs, then clean)
systemd-tmpfiles --create --clean
 
# Dry run
systemd-tmpfiles --create --dry-run
systemd-tmpfiles --clean --dry-run
 
# Remove a specific path
systemd-tmpfiles --remove /tmp/myapp-cache

systemd-tmpfiles.timer (Automatic Cleanup)

tmpfiles cleanup is triggered by a systemd timer:

# The timer runs tmpfiles --clean periodically
systemctl list-timers tmpfiles-clean.timer
# NEXT                        LEFT     LAST                        PASSED   UNIT              ACTIVATES
# Sun 2025-06-08 00:00:00 UTC  12h left  Sat 2025-06-07 00:00:00 UTC  12h ago  tmpfiles-clean.timer tmpfiles-clean.service

The timer runs daily at 00:00:00. The service runs:

systemd-tmpfiles --clean

Files not accessed in the Age period are deleted.

/tmp vs /var/tmp

/tmp — cleared on every reboot (-volatile)
/var/tmp — persists across reboots (semi-persistent)

Default tmpfiles for both:

# From /lib/tmpfiles.d/tmp.conf (Ubuntu default):
q  /tmp  1777  root  root  -
q  /var/tmp  1777  root  root  -
 
# q = create with sticky bit (only owner can delete)
/var/tmp is NOT cleared on reboot by default, only by tmpfiles-clean timer

Custom /tmp on tmpfs

Many distros mount /tmp as tmpfs (in-memory, faster, cleared on reboot):

# /etc/fstab entry:
tmpfs  /tmp  tmpfs  defaults,noatime,mode=1777  0 0
 
# systemd equivalent (in /etc/tmpfiles.d/):
# On some systems tmpfiles.d handles tmpfs mounting:
w  /proc/self/mountinfo  -  -  -  -  ...

Note: tmpfs is controlled by /etc/fstab or /proc/self/mountinfo, not by tmpfiles.d.

Use Cases

1. Your service needs /run/myapp before it starts

# /etc/tmpfiles.d/myapp.conf
d  /run/myapp  0755  myapp  myapp  -

# myapp.service
[Service]
RuntimeDirectory=myapp      # systemd creates /run/myapp automatically
# Equivalent to the tmpfiles.d above

systemd’s RuntimeDirectory= directive replaces tmpfiles.d for simple directory creation in services.

2. Clean up old files in /tmp after 7 days

# /etc/tmpfiles.d/cleanup.conf
r  /tmp/old-app-cache  -  -  -  7d  -
# r = remove file if older than Age

Permissions Note

tmpfiles runs as root early in boot (before services). So it can create files with any ownership. Regular users can’t use tmpfiles.d to create files as root — only root can write to /etc/tmpfiles.d/.

Verification

# List all tmpfiles.d configs
find /etc/tmpfiles.d /run/tmpfiles.d /lib/tmpfiles.d -name "*.conf"
systemd-tmpfiles --cat-config