Question about LTTng Context

Question about LTTng Context

[Amir Najafi Zadeh via lttng-dev]

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Hello everyone,

I hope you’re doing well. My name is Amir, and I’m a PhD student in the
Computer Science department at Stony Brook University, New York.

I have a question about the LTTng context that I haven’t been able to find
an answer for in the docs or man pages. Does LTTng support adding the
cgroup ID or cgroup path as a context field? I want to filter my trace
results based on cgroups.

If this isn’t supported, are there any plans to add it in future versions,
such as 2.14?

For reference, I’m currently using LTTng 2.13 on Ubuntu 24.04 with kernel
6.8.0-87-generic.
Cheers,
Amir
-- 
*Amirhossein Najafizadeh*



*PhD Student, Computer Science Department, Stony Brook University, N.Y.File
systems and Storage Lab (FSL)*
najafizadeh21@gmail.com
https://amirhnajafiz.github.io/

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Re: Question about LTTng Context

[Kienan Stewart via lttng-dev]

Hi Amir,

On 12/10/25 9:40 PM, Amir Najafi Zadeh via lttng-dev wrote:
> Hello everyone,
> 
> I hope you’re doing well. My name is Amir, and I’m a PhD student in the 
> Computer Science department at Stony Brook University, New York.
> 
> I have a question about the LTTng context that I haven’t been able to 
> find an answer for in the docs or man pages. Does LTTng support adding 
> the cgroup ID or cgroup path as a context field? I want to filter my 
> trace results based on cgroups.
> 

I think you're looking for the `cgroup_ns` context which adds the inum 
of the cgroup namespace as a context field.

thanks,
kienan

> If this isn’t supported, are there any plans to add it in future 
> versions, such as 2.14?
> 
> For reference, I’m currently using LTTng 2.13 on Ubuntu 24.04 with 
> kernel 6.8.0-87-generic.
> 
> Cheers,
> Amir
> -- 
> *Amirhossein Najafizadeh*
> *PhD Student, Computer Science Department, Stony Brook University, N.Y.
> File systems and Storage Lab (FSL)
> 
> *
> najafizadeh21@gmail.com <mailto:najafizadeh21@gmail.com>
> https://amirhnajafiz.github.io/ <https://amirhnajafiz.github.io/>

Re: Question about LTTng Context

[Michael Jeanson via lttng-dev]

On 12/11/25 09:30, Kienan Stewart via lttng-dev wrote:
> Hi Amir,
> 
> On 12/10/25 9:40 PM, Amir Najafi Zadeh via lttng-dev wrote:
>> Hello everyone,
>>
>> I hope you’re doing well. My name is Amir, and I’m a PhD student in 
>> the Computer Science department at Stony Brook University, New York.
>>
>> I have a question about the LTTng context that I haven’t been able to 
>> find an answer for in the docs or man pages. Does LTTng support adding 
>> the cgroup ID or cgroup path as a context field? I want to filter my 
>> trace results based on cgroups.
>>
> 
> I think you're looking for the `cgroup_ns` context which adds the inum 
> of the cgroup namespace as a context field.

This will give you the ID of the cgroup namespace but we don't have 
contexts for cgroups themselves. It's probably something we would like 
to have but there is no concrete plans on implementing this at the moment.

> 
>> If this isn’t supported, are there any plans to add it in future 
>> versions, such as 2.14?
>>
>> For reference, I’m currently using LTTng 2.13 on Ubuntu 24.04 with 
>> kernel 6.8.0-87-generic.
>>
>> Cheers,
>> Amir
>> -- 
>> *Amirhossein Najafizadeh*
>> *PhD Student, Computer Science Department, Stony Brook University, N.Y.
>> File systems and Storage Lab (FSL)

Re: Question about LTTng Context

[Amir Najafi Zadeh via lttng-dev]

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Michael, Kienan, Thank you both for your replies. As you mentioned the
cgroup namespace, it isn’t very helpful in some cases. Containers may share
the same cgroup namespace, and the container runtime often avoids giving
each container a private cgroup namespace for performance and security
reasons. Because of this, the cgroup namespace can’t be used as a reliable
or unique label for filtering trace logs.

In my case, with container-d you can inspect a container, find its PID, and
then check /proc/<pid>/ns/cgroup, but you’ll see that different containers
often have the same cgroup namespace ID (e.g., in the following logs you
can see the calico-node and kube-proxy containers sharing a cgroup ns).

```
Name: calico-node  CID:
b5624afe31b005725f4ba53c7b6fe758f3c09fabf013085231ff8b97588f6ace  PID: 2243
 cgroup_ns_inode: 4026531835
Name: kube-proxy  CID:
52f3c12def7a680f61a925ac92dd5ebd5eba6cad17d671efbfd1d40db7dff624  PID: 1851
 cgroup_ns_inode: 4026531835
  >> MATCH FOUND: shares ns with container:
b5624afe31b005725f4ba53c7b6fe758f3c09fabf013085231ff8b97588f6ace
(calico-node)
```

Thanks again for your answers. I hope this feature appears in a future
patch.

Best,
Amir

On Thu, Dec 11, 2025 at 9:57 AM Michael Jeanson <mjeanson@efficios.com>
wrote:

> On 12/11/25 09:30, Kienan Stewart via lttng-dev wrote:
> > Hi Amir,
> >
> > On 12/10/25 9:40 PM, Amir Najafi Zadeh via lttng-dev wrote:
> >> Hello everyone,
> >>
> >> I hope you’re doing well. My name is Amir, and I’m a PhD student in
> >> the Computer Science department at Stony Brook University, New York.
> >>
> >> I have a question about the LTTng context that I haven’t been able to
> >> find an answer for in the docs or man pages. Does LTTng support adding
> >> the cgroup ID or cgroup path as a context field? I want to filter my
> >> trace results based on cgroups.
> >>
> >
> > I think you're looking for the `cgroup_ns` context which adds the inum
> > of the cgroup namespace as a context field.
>
> This will give you the ID of the cgroup namespace but we don't have
> contexts for cgroups themselves. It's probably something we would like
> to have but there is no concrete plans on implementing this at the moment.
>
> >
> >> If this isn’t supported, are there any plans to add it in future
> >> versions, such as 2.14?
> >>
> >> For reference, I’m currently using LTTng 2.13 on Ubuntu 24.04 with
> >> kernel 6.8.0-87-generic.
> >>
> >> Cheers,
> >> Amir
> >> --
> >> *Amirhossein Najafizadeh*
> >> *PhD Student, Computer Science Department, Stony Brook University, N.Y.
> >> File systems and Storage Lab (FSL)
>

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Re: Question about LTTng Context

[Michael Jeanson via lttng-dev]

On 12/11/25 10:51, Amir Najafi Zadeh wrote:
> Michael, Kienan, Thank you both for your replies. As you mentioned the 
> cgroup namespace, it isn’t very helpful in some cases. Containers may 
> share the same cgroup namespace, and the container runtime often avoids 
> giving each container a private cgroup namespace for performance and 
> security reasons. Because of this, the cgroup namespace can’t be used as 
> a reliable or unique label for filtering trace logs.
> 
> In my case, with container-d you can inspect a container, find its PID, 
> and then check /proc/<pid>/ns/cgroup, but you’ll see that different 
> containers often have the same cgroup namespace ID (e.g., in the 
> following logs you can see the calico-node and kube-proxy containers 
> sharing a cgroup ns).

If you want to track containers, the pid namespace is the one used by 
most container runtimes but I don't know specifically for container-d.

> 
> ```
> Name: calico-node  CID: 
> b5624afe31b005725f4ba53c7b6fe758f3c09fabf013085231ff8b97588f6ace  PID: 
> 2243  cgroup_ns_inode: 4026531835
> Name: kube-proxy  CID: 
> 52f3c12def7a680f61a925ac92dd5ebd5eba6cad17d671efbfd1d40db7dff624  PID: 
> 1851  cgroup_ns_inode: 4026531835
>    >> MATCH FOUND: shares ns with container: 
> b5624afe31b005725f4ba53c7b6fe758f3c09fabf013085231ff8b97588f6ace 
> (calico-node)
> ```
> 
> Thanks again for your answers. I hope this feature appears in a future 
> patch.
> 
> Best,
> Amir
> 
> On Thu, Dec 11, 2025 at 9:57 AM Michael Jeanson <mjeanson@efficios.com 
> <mailto:mjeanson@efficios.com>> wrote:
> 
>     On 12/11/25 09:30, Kienan Stewart via lttng-dev wrote:
>      > Hi Amir,
>      >
>      > On 12/10/25 9:40 PM, Amir Najafi Zadeh via lttng-dev wrote:
>      >> Hello everyone,
>      >>
>      >> I hope you’re doing well. My name is Amir, and I’m a PhD student in
>      >> the Computer Science department at Stony Brook University, New York.
>      >>
>      >> I have a question about the LTTng context that I haven’t been
>     able to
>      >> find an answer for in the docs or man pages. Does LTTng support
>     adding
>      >> the cgroup ID or cgroup path as a context field? I want to
>     filter my
>      >> trace results based on cgroups.
>      >>
>      >
>      > I think you're looking for the `cgroup_ns` context which adds the
>     inum
>      > of the cgroup namespace as a context field.
> 
>     This will give you the ID of the cgroup namespace but we don't have
>     contexts for cgroups themselves. It's probably something we would like
>     to have but there is no concrete plans on implementing this at the
>     moment.
> 
>      >
>      >> If this isn’t supported, are there any plans to add it in future
>      >> versions, such as 2.14?
>      >>
>      >> For reference, I’m currently using LTTng 2.13 on Ubuntu 24.04 with
>      >> kernel 6.8.0-87-generic.
>      >>
>      >> Cheers,
>      >> Amir
>      >> --
>      >> *Amirhossein Najafizadeh*
>      >> *PhD Student, Computer Science Department, Stony Brook
>     University, N.Y.
>      >> File systems and Storage Lab (FSL)
> 

Re: Question about LTTng Context

[Amir Najafi Zadeh via lttng-dev]

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I'll try that too. Thanks for mentioning it.

Cheers,
Amir

On Thu, 11 Dec 2025, 11:14 Michael Jeanson, <mjeanson@efficios.com> wrote:

> On 12/11/25 10:51, Amir Najafi Zadeh wrote:
> > Michael, Kienan, Thank you both for your replies. As you mentioned the
> > cgroup namespace, it isn’t very helpful in some cases. Containers may
> > share the same cgroup namespace, and the container runtime often avoids
> > giving each container a private cgroup namespace for performance and
> > security reasons. Because of this, the cgroup namespace can’t be used as
> > a reliable or unique label for filtering trace logs.
> >
> > In my case, with container-d you can inspect a container, find its PID,
> > and then check /proc/<pid>/ns/cgroup, but you’ll see that different
> > containers often have the same cgroup namespace ID (e.g., in the
> > following logs you can see the calico-node and kube-proxy containers
> > sharing a cgroup ns).
>
> If you want to track containers, the pid namespace is the one used by
> most container runtimes but I don't know specifically for container-d.
>
> >
> > ```
> > Name: calico-node  CID:
> > b5624afe31b005725f4ba53c7b6fe758f3c09fabf013085231ff8b97588f6ace  PID:
> > 2243  cgroup_ns_inode: 4026531835
> > Name: kube-proxy  CID:
> > 52f3c12def7a680f61a925ac92dd5ebd5eba6cad17d671efbfd1d40db7dff624  PID:
> > 1851  cgroup_ns_inode: 4026531835
> >    >> MATCH FOUND: shares ns with container:
> > b5624afe31b005725f4ba53c7b6fe758f3c09fabf013085231ff8b97588f6ace
> > (calico-node)
> > ```
> >
> > Thanks again for your answers. I hope this feature appears in a future
> > patch.
> >
> > Best,
> > Amir
> >
> > On Thu, Dec 11, 2025 at 9:57 AM Michael Jeanson <mjeanson@efficios.com
> > <mailto:mjeanson@efficios.com>> wrote:
> >
> >     On 12/11/25 09:30, Kienan Stewart via lttng-dev wrote:
> >      > Hi Amir,
> >      >
> >      > On 12/10/25 9:40 PM, Amir Najafi Zadeh via lttng-dev wrote:
> >      >> Hello everyone,
> >      >>
> >      >> I hope you’re doing well. My name is Amir, and I’m a PhD student
> in
> >      >> the Computer Science department at Stony Brook University, New
> York.
> >      >>
> >      >> I have a question about the LTTng context that I haven’t been
> >     able to
> >      >> find an answer for in the docs or man pages. Does LTTng support
> >     adding
> >      >> the cgroup ID or cgroup path as a context field? I want to
> >     filter my
> >      >> trace results based on cgroups.
> >      >>
> >      >
> >      > I think you're looking for the `cgroup_ns` context which adds the
> >     inum
> >      > of the cgroup namespace as a context field.
> >
> >     This will give you the ID of the cgroup namespace but we don't have
> >     contexts for cgroups themselves. It's probably something we would
> like
> >     to have but there is no concrete plans on implementing this at the
> >     moment.
> >
> >      >
> >      >> If this isn’t supported, are there any plans to add it in future
> >      >> versions, such as 2.14?
> >      >>
> >      >> For reference, I’m currently using LTTng 2.13 on Ubuntu 24.04
> with
> >      >> kernel 6.8.0-87-generic.
> >      >>
> >      >> Cheers,
> >      >> Amir
> >      >> --
> >      >> *Amirhossein Najafizadeh*
> >      >> *PhD Student, Computer Science Department, Stony Brook
> >     University, N.Y.
> >      >> File systems and Storage Lab (FSL)
> >
>
>

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