docs: describe valid unit names in systemd.unit(5)

2 files changed, 21 insertions, 10 deletions

diff --git a/man/systemd.unit.xml b/man/systemd.unit.xml
index 8307be1d33..acb09d005d 100644
--- a/man/systemd.unit.xml
+++ b/man/systemd.unit.xml
@@ -104,16 +104,24 @@
     <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
     </para>
 
-    <para>Unit files are loaded from a set of paths determined during
-    compilation, described in the next section.</para>
-
-    <para>Unit files can be parameterized by a single argument called the "instance name". The unit
-    is then constructed based on a "template file" which serves as the definition of multiple
-    services or other units. A template unit must have a single <literal>@</literal> at the end of
-    the name (right before the type suffix). The name of the full unit is formed by inserting the
-    instance name between <literal>@</literal> and the unit type suffix. In the unit file itself,
-    the instance parameter may be referred to using <literal>%i</literal> and other specifiers, see
-    below.</para>
+    <para>Unit files are loaded from a set of paths determined during compilation, described in the next
+    section.</para>
+
+    <para>Valid unit names consist of a "name prefix" and a dot and a suffix specifying the unit type. The
+    "unit prefix" must consist of one or more valid characters (ASCII letters, digits, <literal>:</literal>,
+    <literal>-</literal>, <literal>_</literal>, <literal>.</literal>, and <literal>\</literal>). The total
+    length of the unit name including the suffix must not exceed 256 characters. The type suffix must be one
+    of <literal>.service</literal>, <literal>.socket</literal>, <literal>.device</literal>,
+    <literal>.mount</literal>, <literal>.automount</literal>, <literal>.swap</literal>,
+    <literal>.target</literal>, <literal>.path</literal>, <literal>.timer</literal>,
+    <literal>.slice</literal>, or <literal>.scope</literal>.</para>
+
+    <para>Units names can be parameterized by a single argument called the "instance name". The unit is then
+    constructed based on a "template file" which serves as the definition of multiple services or other
+    units. A template unit must have a single <literal>@</literal> at the end of the name (right before the
+    type suffix). The name of the full unit is formed by inserting the instance name between
+    <literal>@</literal> and the unit type suffix. In the unit file itself, the instance parameter may be
+    referred to using <literal>%i</literal> and other specifiers, see below.</para>
 
     <para>Unit files may contain additional options on top of those
     listed here. If systemd encounters an unknown option, it will
diff --git a/src/test/test-unit-name.c b/src/test/test-unit-name.c
index 7fe732cf2f..25c649828e 100644
--- a/src/test/test-unit-name.c
+++ b/src/test/test-unit-name.c
@@ -50,6 +50,9 @@ static void test_unit_name_is_valid(void) {
         assert_se(!unit_name_is_valid("foo@.service", UNIT_NAME_INSTANCE));
         assert_se( unit_name_is_valid("foo@.service", UNIT_NAME_TEMPLATE));
         assert_se( unit_name_is_valid("foo@.service", UNIT_NAME_INSTANCE|UNIT_NAME_TEMPLATE));
+        assert_se( unit_name_is_valid(".test.service", UNIT_NAME_PLAIN));
+        assert_se( unit_name_is_valid(".test@.service", UNIT_NAME_TEMPLATE));
+        assert_se( unit_name_is_valid("_strange::::.service", UNIT_NAME_ANY));
 
         assert_se(!unit_name_is_valid(".service", UNIT_NAME_ANY));
         assert_se(!unit_name_is_valid("", UNIT_NAME_ANY));