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), systemd.nspawn(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)

       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/