[PATCH] man/man5/tmpfs.5: Specify that noswap may not be used within unprivileged user namespaces

[PATCH] man/man5/tmpfs.5: Specify that noswap may not be used within unprivileged user namespaces

[Grayson Tinker]

Since the tmpfs noswap option was added, the kernel has disallowed its use while
within an unprivileged user namespace for security reasons. Document this restriction
so users do not believe noswap to be available in every situation.

ref. linux.git 01106e140835ff94fdef79d66f166b87b0c89824 ("shmem: restrict noswap option to initial user namespace")

Signed-off-by: Grayson Tinker <graysontinker@gmail.com>
---
 man/man5/tmpfs.5 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/man/man5/tmpfs.5 b/man/man5/tmpfs.5
index 10acbdcfa..a904db2c8 100644
--- a/man/man5/tmpfs.5
+++ b/man/man5/tmpfs.5
@@ -109,6 +109,10 @@ but not a % suffix.
 Disables swap.
 Remounts must respect the original settings.
 By default swap is enabled.
+.IP
+.\" commit 01106e140835ff94fdef79d66f166b87b0c89824
+.B noswap
+is not available while within an unprivileged user namespace.
 .TP
 .BR mode =\f[I]mode\f[]
 Set initial permissions of the root directory.

Range-diff:
-:  --------- > 1:  b3b2becca man/man5/tmpfs.5: Specify that noswap may not be used within unprivileged user namespaces
-- 
2.55.0

Re: [PATCH] man/man5/tmpfs.5: Specify that noswap may not be used within unprivileged user namespaces

[Alejandro Colomar]

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Hi Grayson,

> Date: 2026-10-19 19:51:12-0600
> From: Grayson Tinker <graysontinker@gmail.com>
>
> Since the tmpfs noswap option was added, the kernel has disallowed its use while
> within an unprivileged user namespace for security reasons. Document this restriction
> so users do not believe noswap to be available in every situation.
> 
> ref. linux.git 01106e140835ff94fdef79d66f166b87b0c89824 ("shmem: restrict noswap option to initial user namespace")
> 
> Signed-off-by: Grayson Tinker <graysontinker@gmail.com>

Thanks!  I've applied the patch.


Have a lovely night!
Alex

> ---
>  man/man5/tmpfs.5 | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/man/man5/tmpfs.5 b/man/man5/tmpfs.5
> index 10acbdcfa..a904db2c8 100644
> --- a/man/man5/tmpfs.5
> +++ b/man/man5/tmpfs.5
> @@ -109,6 +109,10 @@ but not a % suffix.
>  Disables swap.
>  Remounts must respect the original settings.
>  By default swap is enabled.
> +.IP
> +.\" commit 01106e140835ff94fdef79d66f166b87b0c89824
> +.B noswap
> +is not available while within an unprivileged user namespace.
>  .TP
>  .BR mode =\f[I]mode\f[]
>  Set initial permissions of the root directory.
> 
> Range-diff:
> -:  --------- > 1:  b3b2becca man/man5/tmpfs.5: Specify that noswap may not be used within unprivileged user namespaces
> -- 
> 2.55.0
> 

-- 
<https://www.alejandro-colomar.es>

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