NAME

       systemd.syntax - General syntax of systemd configuration files

INTRODUCTION

       This page describes the basic principles of configuration files used by systemd(1) and related programs
       for:

       •   systemd unit files, see systemd.unit(5), systemd.service(5), systemd.socket(5), systemd.device(5),
           systemd.mount(5), systemd.automount(5), systemd.swap(5), systemd.target(5), systemd.path(5),
           systemd.timer(5), systemd.slice(5), systemd.scope(5)

       •   link files, see systemd.link(5)

       •   netdev and network files, see systemd.netdev(5), systemd.network(5)

       •   daemon config files, see systemd-system.conf(5), systemd-user.conf(5), logind.conf(5),
           journald.conf(5), journal-remote.conf(5), journal-upload.conf(5), systemd-sleep.conf(5),
           timesyncd.conf(5)

       •   nspawn files, see systemd.nspawn(5)

       The syntax is inspired by XDG Desktop Entry Specification[1] .desktop files, which are in turn inspired
       by Microsoft Windows .ini files.

       Each file is a plain text file divided into sections, with configuration entries in the style key=value.
       Whitespace immediately before or after the "=" is ignored. Empty lines and lines starting with "#" or ";"
       are ignored, which may be used for commenting.

       Lines ending in a backslash are concatenated with the following line while reading and the backslash is
       replaced by a space character. This may be used to wrap long lines. The limit on line length is very
       large (currently 1 MB), but it is recommended to avoid such long lines and use multiple directives,
       variable substitution, or other mechanism as appropriate for the given file type. When a comment line or
       lines follow a line ending with a backslash, the comment block is ignored, so the continued line is
       concatenated with whatever follows the comment block.

       Example 1.

           [Section A]
           KeyOne=value 1
           KeyTwo=value 2

           # a comment

           [Section B]
           Setting="something" "some thing" "..."
           KeyTwo=value 2 \
                  value 2 continued

           [Section C]
           KeyThree=value 3\
           # this line is ignored
           ; this line is ignored too
                  value 3 continued

       Boolean arguments used in configuration files can be written in various formats. For positive settings
       the strings 1, yes, true and on are equivalent. For negative settings, the strings 0, no, false and off
       are equivalent.

       Time span values encoded in configuration files can be written in various formats. A stand-alone number
       specifies a time in seconds. If suffixed with a time unit, the unit is honored. A concatenation of
       multiple values with units is supported, in which case the values are added up. Example: "50" refers to
       50 seconds; "2min 200ms" refers to 2 minutes and 200 milliseconds, i.e. 120200 ms. The following time
       units are understood: "s", "min", "h", "d", "w", "ms", "us". For details see systemd.time(7).

       Various settings are allowed to be specified more than once, in which case the interpretation depends on
       the setting. Often, multiple settings form a list, and setting to an empty value "resets", which means
       that previous assignments are ignored. When this is allowed, it is mentioned in the description of the
       setting. Note that using multiple assignments to the same value makes the file incompatible with parsers
       for the XDG .desktop file format.

QUOTING

       For settings where quoting is allowed, the following general rules apply: double quotes ("...") and
       single quotes ('...') may be used to wrap a whole item (the opening quote may appear only at the
       beginning or after whitespace that is not quoted, and the closing quote must be followed by whitespace or
       the end of line), in which case everything until the next matching quote becomes part of the same item.
       Quotes themselves are removed. C-style escapes are supported. The table below contains the list of known
       escape patterns. Only escape patterns which match the syntax in the table are allowed; other patterns may
       be added in the future and unknown patterns will result in a warning. In particular, any backslashes
       should be doubled. Finally, a trailing backslash ("\") may be used to merge lines, as described above.
       UTF-8 is accepted, and hence typical unicode characters do not need to be escaped.

       Table 1. Supported escapes
       ┌─────────────┬────────────────────────────────────┐
       │Literal      │ Actual value                       │
       ├─────────────┼────────────────────────────────────┤
       │"\a"         │ bell                               │
       ├─────────────┼────────────────────────────────────┤
       │"\b"         │ backspace                          │
       ├─────────────┼────────────────────────────────────┤
       │"\f"         │ form feed                          │
       ├─────────────┼────────────────────────────────────┤
       │"\n"         │ newline                            │
       ├─────────────┼────────────────────────────────────┤
       │"\r"         │ carriage return                    │
       ├─────────────┼────────────────────────────────────┤
       │"\t"         │ tab                                │
       ├─────────────┼────────────────────────────────────┤
       │"\v"         │ vertical tab                       │
       ├─────────────┼────────────────────────────────────┤
       │"\\"         │ backslash                          │
       ├─────────────┼────────────────────────────────────┤
       │"\""         │ double quotation mark              │
       ├─────────────┼────────────────────────────────────┤
       │"\'"         │ single quotation mark              │
       ├─────────────┼────────────────────────────────────┤
       │"\s"         │ space                              │
       ├─────────────┼────────────────────────────────────┤
       │"\xxx"       │ character number xx in hexadecimal │
       │             │ encoding                           │
       ├─────────────┼────────────────────────────────────┤
       │"\nnn"       │ character number nnn in octal      │
       │             │ encoding                           │
       ├─────────────┼────────────────────────────────────┤
       │"\unnnn"     │ unicode code point nnnn in         │
       │             │ hexadecimal encoding               │
       ├─────────────┼────────────────────────────────────┤
       │"\Unnnnnnnn" │ unicode code point nnnnnnnn in     │
       │             │ hexadecimal encoding               │
       └─────────────┴────────────────────────────────────┘

SEE ALSO

       systemd.time(7)

NOTES

        1. XDG Desktop Entry Specification
           https://standards.freedesktop.org/desktop-entry-spec/latest/