A systemd-tmpfiles rule has seven fields, in this order: Type Path Mode User Group Age Argument. The type determines the operation and which of the other fields apply; a dash (-) generally means a field is unspecified, not that a value should be erased.
The seven fields, from left to right
The field layout documented in Debian testing’s tmpfiles.d(5) manual is:
Type Path Mode User Group Age Argument| Field | Meaning | How to interpret it |
|---|---|---|
Type |
The operation | A letter such as d or L, optionally followed by supported modifiers. The type determines which remaining fields matter. |
Path |
The filesystem target | The file or directory to act on; some rule types also accept glob patterns. Do not assume every path is treated as a glob. |
Mode |
Access permissions | An octal mode such as 0755, when relevant to the type. - leaves it unspecified. |
User |
Owner | A user name for types that apply ownership. - leaves it unspecified. |
Group |
Group owner | A group name for types that apply ownership. - leaves it unspecified. |
Age |
Cleanup threshold | Used by applicable rules during cleanup; it is not a timer that applies to every rule. |
Argument |
Additional type-specific data | For example, a symlink destination or content to write. It occupies the seventh field and has special whitespace handling. |
These meanings are not universal instructions to set every value on every line. Consult the installed tmpfiles.d(5) manual for the exact behavior of a type and any modifiers your system supports.
How the fields work in real rules
Directory rule
d /run/user 0755 root root 10d -d selects directory creation or management, and /run/user is the target. 0755 is the mode; root root specify user and group. 10d is an age value for applicable cleanup behavior, while the final - leaves the argument unused. This is a syntax example from the tmpfiles.d manual, not a claim that the directory is necessarily removed after ten days in every situation.
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Symlink rule
L /tmp/foobar - - - - /dev/nullL selects the symlink operation, and /tmp/foobar is the link path. The four dashes leave mode, user, group, and age unspecified; /dev/null is the type-specific argument giving the link destination.
Parsing details that can change how a line reads
- Each rule occupies a line; whitespace separates fields.
- Fields can contain C-style escapes. Fields other than the seventh argument may also be quoted.
- The seventh field is special: after the argument starts, the remaining text belongs to it, including whitespace. To make an argument begin with whitespace, use a C-style escape such as
x20. - A type that does not define an argument rejects a non-empty argument. Use
-where the argument should be empty. - Some types accept glob patterns in the path field; glob behavior is type-dependent.
- Modifier characters can appear with a type, but supported combinations and their effects depend on the systemd version. Check the local manual rather than assuming a modifier behaves identically across distributions.
When tmpfiles rules take effect
The systemd-tmpfiles manual describes the utility as creating, deleting, and cleaning up files and directories using the configuration format and locations defined by tmpfiles.d(5). Invocations such as --create, --remove, and --clean select operation sets. Cleanup is concerned with entries that have applicable age parameters; an age value does not make every rule a scheduled deletion.
System services process system configuration. User services read separate user configuration locations and do not control global cleanup for the system instance.
Quick Recap
Best Value
Rank #4
How to read or compare two rules safely
- Read the type first to identify the operation and determine which fields apply.
- Check the path to see exactly which target—or, where supported, which matching paths—is affected.
- Interpret mode, user, and group as metadata settings only where that operation uses them; treat dashes as unspecified fields.
- Read age as a cleanup parameter only for applicable types.
- Interpret the final argument according to the type, keeping its special whitespace parsing in mind.
- For a rule on a particular machine, consult
man tmpfiles.dand checksystemd-tmpfiles --version. Distribution manuals can describe a different systemd version from the one installed on the host.
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