Re: Question about LTTng Context

[Michael Jeanson via lttng-dev <lttng-dev@lists.lttng.org>]

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)
>