fstab.5 mount.8: add note about field separator

The value of the mount option X-mount.idmap= can contain spaces as
separators between mappings. Unfortunately, this conflicts with the
fstab format where fields are separated by spaces. Using quotes does
not solve this issue because fields are separated before they are
parsed.

This limitation of the fstab parser within libmount is due to backward
compatibility. The fstab format is a de-facto standard and is parsed
by many tools and libraries, including third-party shell scripts. It
would not be practical to introduce any improvements in libmount that
would make fstabs unparseable in other places.

Users must understand that in-field spaces must be escaped by \040.
For example, X-mount.idmap="0:0:1\040500:1000:1".

Addresses: https://github.com/util-linux/util-linux/issues/2829
Signed-off-by: Karel Zak <kzak@redhat.com>
(cherry picked from commit 52dc9260d469a3731f49c5a78b23f38f2314789e)

diff --git a/sys-utils/fstab.5.adoc b/sys-utils/fstab.5.adoc
index 0f12560e3bc46b128cf0c55d9c1dcdcb5f7744a8..fb649d5f21ab6de34d480c19ed56fc8dcc591500 100644 (file)
--- a/sys-utils/fstab.5.adoc
+++ b/sys-utils/fstab.5.adoc
@@ -54,7 +54,9 @@ The file *fstab* contains descriptive information about the filesystems the syst
 
 The file is not read by *mount*(8) only but often is used by many other tools and daemons, and proper functionality may require additional steps. For example, on systemd-based systems, it's recommended to use *systemctl daemon-reload* after *fstab* modification.
 
-Each filesystem is described on a separate line. Fields on each line are separated by tabs or spaces. Lines starting with '#' are comments. Blank lines are ignored.
+Each filesystem is described on a separate line, with fields separated by tabs or spaces. The line is split into fields before being parsed. This means that any spaces or tabs within the fields must be escaped using \040 or \011, even within quoted strings (e.g. LABEL="foo\040bar").
+
+Lines starting with '#' are comments. Blank lines are ignored.
 
 The following is a typical example of an *fstab* entry:
 

diff --git a/sys-utils/mount.8.adoc b/sys-utils/mount.8.adoc
index ba8b45a2a2a7c505273ff596d9348d03f572bdd8..fc2a83e7534ca2fd314a2c7b9a151bd399fa5209 100644 (file)
--- a/sys-utils/mount.8.adoc
+++ b/sys-utils/mount.8.adoc
@@ -739,7 +739,8 @@ The __id-mount__ parameter indicates the starting ID in the new mount.
 The __id-host__ parameter indicates the starting ID in the filesystem.
 The __id-range__ parameter indicates how many IDs are to be mapped.
 It is possible to specify multiple ID-mappings.
-The individual ID-mappings must be separated by spaces.
++
+The individual ID mappings must be separated by spaces. Please note that in the __/etc/fstab__ file, spaces are interpreted as separators between fields. To avoid this, you must escape them using \040. For example, X-mount.idmap=0:0:1\040500:1000:1.
 +
 For example, the ID-mapping *X-mount.idmap=u:1000:0:1 g:1001:1:2 5000:1000:2* creates an idmapped mount where
 UID 0 is mapped to UID 1000, GID 1 is mapped to GUID 1001, GID 2 is mapped to GID 1002, UID and GID 1000 are mapped to 5000, and UID and GID 1001 are mapped to 5001 in the mount.