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hostname: explain a bit why hostnames should be single DNS labels, not fqdns

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(cherry picked from commit 4362d942c4)
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Lennart Poettering
2025-12-10 10:03:47 +09:00
committed by Luca Boccassi
parent 803ef2a579
commit 0fb453ebd0
1 changed files with 6 additions and 4 deletions
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10
man/hostname.xml
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@@ -38,10 +38,12 @@
<para>The file should contain a single newline-terminated hostname string. Comments (lines starting with
a <literal>#</literal>) are ignored. The hostname should be composed of up to 64 7-bit ASCII lower-case
alphanumeric characters or hyphens forming a valid DNS domain name. It is recommended that this name
contains only a single label, i.e. without any dots. Invalid characters will be filtered out in an
attempt to make the name valid, but obviously it is recommended to use a valid name and not rely on this
filtering.</para>
alphanumeric characters or hyphens forming a valid DNS domain name. It is strongly recommended that this
name contains only a single DNS label, i.e does not contain any dots. This recommendation reflects both
usual expectations of applications, and the fact that the Linux kernel limits the length of the system
hostname to 64 (i.e. close to the maximum DNS label length of 63) rather than 255 (the maximum DNS domain
name length). When applied, invalid characters will be filtered out in an attempt to make the name valid,
but obviously it is recommended to use a valid name and not rely on this filtering.</para>
<para id="question-mark-hostname-pattern">If the question mark character <literal>?</literal> appears in
the hostname, it is automatically substituted by a hexadecimal character derived from the