Cannot allocate memory when calling unshare

Cannot allocate memory when calling unshare

[Andy Johnson]

Hello,
I use git last update of util-linux.

./unshare -n /bin/bash
works ok.

>From a different terminal I run:

./unshare -p /bin/bash
and get:
bash: fork: Cannot allocate memory

typing:
shows 141 Mb free.

the machine has x86_64 ubuntu, 13.04, Raring Ringtail

any advice ?

Best,

Andy

Re: Cannot allocate memory when calling unshare

[Eric W. Biederman]

Andy Johnson <johnsonzjo@gmail.com> writes:

> Hello,
> I use git last update of util-linux.
>
> ./unshare -n /bin/bash
> works ok.
>
> From a different terminal I run:
>
> ./unshare -p /bin/bash
> and get:
> bash: fork: Cannot allocate memory
>
> typing:
> shows 141 Mb free.
>
> the machine has x86_64 ubuntu, 13.04, Raring Ringtail
>
> any advice ?

Pid namespaces are funny.  What you are seeing is expected and correct
behavior.  The process that calls unshare is not put into the pid
namespace it's first child is.  Which means that the first child of bash
becomes the init in the pid namespace and the next child of bash.

The following should do what you want.
unshare --pid -- /bin/sh -c /bin/bash

Eric

Re: Cannot allocate memory when calling unshare

[Andy Johnson]

Thanks.
Copy ans paste of that line:
unshare --pid -- /bin/sh -c /bin/bash

still gave:
./unshare --pid -- /bin/sh -c /bin/bash
bash: fork: Cannot allocate memory

also tried to tweak a bit and it did not help
I am using latest git linux-util on fedora 18 with 3.8.4-202.fc18.x86_64 kernel

regards,
Andy


On Thu, May 9, 2013 at 9:26 PM, Eric W. Biederman <ebiederm@xmission.com> wrote:
> Andy Johnson <johnsonzjo@gmail.com> writes:
>
>> Hello,
>> I use git last update of util-linux.
>>
>> ./unshare -n /bin/bash
>> works ok.
>>
>> From a different terminal I run:
>>
>> ./unshare -p /bin/bash
>> and get:
>> bash: fork: Cannot allocate memory
>>
>> typing:
>> shows 141 Mb free.
>>
>> the machine has x86_64 ubuntu, 13.04, Raring Ringtail
>>
>> any advice ?
>
> Pid namespaces are funny.  What you are seeing is expected and correct
> behavior.  The process that calls unshare is not put into the pid
> namespace it's first child is.  Which means that the first child of bash
> becomes the init in the pid namespace and the next child of bash.
>
> The following should do what you want.
> unshare --pid -- /bin/sh -c /bin/bash
>
> Eric

Re: Cannot allocate memory when calling unshare

[Eric W. Biederman]

Andy Johnson <johnsonzjo@gmail.com> writes:

> Thanks.
> Copy ans paste of that line:
> unshare --pid -- /bin/sh -c /bin/bash
>
> still gave:
> ./unshare --pid -- /bin/sh -c /bin/bash
> bash: fork: Cannot allocate memory
>
> also tried to tweak a bit and it did not help
> I am using latest git linux-util on fedora 18 with
> 3.8.4-202.fc18.x86_64 kernel

How weird.  It works here.

My hunch would be that my /bin/sh is dash, and fedora likes to use bash.
It looks like your /bin/sh is exec'ing /bin/bash instead of forking and
execing it.  You can look in another window and confirm that you don't
have two processes doing the work only one.

When it works echo $$ returns 1.

Shrug.

Eric