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Old 03-25-2010, 02:53 PM
Juan Diego
 
Default tmpfs

Good day everyone,

I want to delete the next two lines from my fstab:

none /dev/pts devpts defaults 0 0
none /dev/shm tmpfs defaults 0 0

however I would like to know the secondary effects of doing such
thing, all the information I could get on the internet is that shm is
for POSIX shared memory support and that almost any program actually
use it, for devpts I couldn't find much information about it.

does anyone knows if it is safe to remove those lines from my fstab?

thank you.
 
Old 03-25-2010, 03:01 PM
Jan de Groot
 
Default tmpfs

On Fri, 2010-03-26 at 00:53 +0900, Juan Diego wrote:
> Good day everyone,
>
> I want to delete the next two lines from my fstab:
>
> none /dev/pts devpts defaults 0 0
> none /dev/shm tmpfs defaults 0 0
>
> however I would like to know the secondary effects of doing such
> thing, all the information I could get on the internet is that shm is
> for POSIX shared memory support and that almost any program actually
> use it, for devpts I couldn't find much information about it.
>
> does anyone knows if it is safe to remove those lines from my fstab?
>
> thank you.

/dev/pts is required for virtual terminals like xterm, gnome-terminal
and others. Without that filesystem you can't start a virtual terminal.

/dev/shm is used for shared memory, it's a requirement for NPTL
semaphore functions. Now that /dev is also on tmpfs, I don't know if
it's harmful to remove. The main requirement is that this folder has
1777 permissions.
 
Old 03-25-2010, 03:07 PM
Thomas Bächler
 
Default tmpfs

Am 25.03.2010 16:53, schrieb Juan Diego:
> Good day everyone,
>
> I want to delete the next two lines from my fstab:
>
> none /dev/pts devpts defaults 0 0
> none /dev/shm tmpfs defaults 0 0
>
> however I would like to know the secondary effects of doing such
> thing, all the information I could get on the internet is that shm is
> for POSIX shared memory support and that almost any program actually
> use it, for devpts I couldn't find much information about it.
>
> does anyone knows if it is safe to remove those lines from my fstab?

This is definitely NOT SAFE!

If you don't have /dev/shm, POSIX shared memory will use the same tmpfs
filesystem as /dev, which is currently limited to 10MB - POSIX shared
memory blocks might be much larger.

As for removing /dev/pts, I was tempted to tell you to do it, as it's SO
funny what happens: No pseudo TTYs are available anymore. This will
effectively prevent ssh logins, screen, any X terminal and probably many
more applications from allocating a TTY, so the only way to get a shell
is to login via a real TTY (console).

I am curious, why would you want to remove these? I am glad thouh that
you asked BEFORE killing your system instead of after.
 
Old 03-25-2010, 03:12 PM
Xavier Chantry
 
Default tmpfs

On Thu, Mar 25, 2010 at 5:07 PM, Thomas Bächler <thomas@archlinux.org> wrote:
>
> This is definitely NOT SAFE!
>
> If you don't have /dev/shm, POSIX shared memory will use the same tmpfs
> filesystem as /dev, which is currently limited to 10MB - POSIX shared
> memory blocks might be much larger.
>
> As for removing /dev/pts, I was tempted to tell you to do it, as it's SO
> funny what happens: No pseudo TTYs are available anymore. This will
> effectively prevent ssh logins, screen, any X terminal and probably many
> more applications from allocating a TTY, so the only way to get a shell
> is to login via a real TTY (console).
>
> I am curious, why would you want to remove these? I am glad thouh that
> you asked BEFORE killing your system instead of after.
>
>

Random suggestion : adding a one-line comment before these two entries
describing what they are for (i.e. sumup of the above)
 
Old 03-25-2010, 03:22 PM
Thomas Bächler
 
Default tmpfs

Am 25.03.2010 17:12, schrieb Xavier Chantry:
> On Thu, Mar 25, 2010 at 5:07 PM, Thomas Bächler <thomas@archlinux.org> wrote:
>>
>> This is definitely NOT SAFE!
>>
>> If you don't have /dev/shm, POSIX shared memory will use the same tmpfs
>> filesystem as /dev, which is currently limited to 10MB - POSIX shared
>> memory blocks might be much larger.
>>
>> As for removing /dev/pts, I was tempted to tell you to do it, as it's SO
>> funny what happens: No pseudo TTYs are available anymore. This will
>> effectively prevent ssh logins, screen, any X terminal and probably many
>> more applications from allocating a TTY, so the only way to get a shell
>> is to login via a real TTY (console).
>>
>> I am curious, why would you want to remove these? I am glad thouh that
>> you asked BEFORE killing your system instead of after.
>>
>>
>
> Random suggestion : adding a one-line comment before these two entries
> describing what they are for (i.e. sumup of the above)

Patches welcome.

Personally, I don't think it's worth the time - anyone who is going to
mess with these entries is either expected to know what they are for or
fail miserably. However, as someone who has been messing with this stuff
for 10 years, I am probably not the right person to ask.
 
Old 03-25-2010, 03:47 PM
Juan Diego
 
Default tmpfs

I wanted to remove them because I was cleaning my fstab of old entries
that I dont use anymore, so I found those two in the middle of the
way, I guess they will have to stay there

On Fri, Mar 26, 2010 at 1:22 AM, Thomas Bächler <thomas@archlinux.org> wrote:
> Am 25.03.2010 17:12, schrieb Xavier Chantry:
>> On Thu, Mar 25, 2010 at 5:07 PM, Thomas Bächler <thomas@archlinux.org> wrote:
>>>
>>> This is definitely NOT SAFE!
>>>
>>> If you don't have /dev/shm, POSIX shared memory will use the same tmpfs
>>> filesystem as /dev, which is currently limited to 10MB - POSIX shared
>>> memory blocks might be much larger.
>>>
>>> As for removing /dev/pts, I was tempted to tell you to do it, as it's SO
>>> funny what happens: No pseudo TTYs are available anymore. This will
>>> effectively prevent ssh logins, screen, any X terminal and probably many
>>> more applications from allocating a TTY, so the only way to get a shell
>>> is to login via a real TTY (console).
>>>
>>> I am curious, why would you want to remove these? I am glad thouh that
>>> you asked BEFORE killing your system instead of after.
>>>
>>>
>>
>> Random suggestion : adding a one-line comment before these two entries
>> describing what they are for (i.e. sumup of the above)
>
> Patches welcome.
>
> Personally, I don't think it's worth the time - anyone who is going to
> mess with these entries is either expected to know what they are for or
> fail miserably. However, as someone who has been messing with this stuff
> for 10 years, I am probably not the right person to ask.
>
>
 
Old 03-25-2010, 09:44 PM
Ng Oon-Ee
 
Default tmpfs

On Fri, 2010-03-26 at 01:47 +0900, Juan Diego wrote:
> I wanted to remove them because I was cleaning my fstab of old entries
> that I dont use anymore, so I found those two in the middle of the
> way, I guess they will have to stay there

Bottom-posting, please...

And yes, I've wanted to remove them before. Thankfully google set me
right on that one.
 

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