On Sun, Nov 1, 2015 at 12:25 PM, Richard Weinberger <richard.weinberger@xxxxxxxxx> wrote: > On Sat, Oct 24, 2015 at 11:54 PM, Shayan Pooya <shayan@xxxxxxxxxx> wrote: >> I noticed the following core_pattern behavior in my linux box while >> running docker containers. I am not sure if it is bug, but it is >> inconsistent and not documented. >> >> If the core_pattern is set on the host, the containers will observe >> and use the pattern for dumping cores (there is no per cgroup >> core_pattern). According to core(5) for setting core_pattern one can: >> >> 1. echo "/tmp/cores/core.%e.%p" > /proc/sys/kernel/core_pattern >> 2. echo "|/bin/custom_core /tmp/cores/ %e %p " > /proc/sys/kernel/core_pattern >> >> The former pattern evaluates the /tmp/cores path in the container's >> filesystem namespace. Which means, the host does not see a core file >> in /tmp/cores. >> >> However, the latter evaluates the /bin/custom_core path in the global >> filesystem namespace. Moreover, if /bin/core decides to write the core >> to a path (/tmp/cores in this case as shown by the arg to >> custom_core), the path will be evaluated in the global filesystem >> namespace as well. >> >> The latter behaviour is counter-intuitive and error-prone as the >> container can fill up the core-file directory which it does not have >> direct access to (which means the core is also not accessible for >> debugging if someone only has access to the container). >> >> Currently, I work around this issue by detecting that the process is >> crashing from a container (by comparing the namespace pid to the >> global pid) and refuse to dump the core if it is from a container. > > IMHO this is another example of the question whether a container should > be a full blown Linux system or not. I'd like to use containers as a way for separating concerns (IMHO this is a popular use case for the containers, e.g. redhat's openshift). The processes running inside a namespace should be that namespace's problem. > In your opinion containers should own core_pattern and be able to install > their own dump helpers. Well, it is not just my opinion. That's the default behaviour for when you don't use a pipe in the core_pattern. The reason I'd say it is a bug is because the two options are not consistent. > Currently this is not the case as this is setting is only writable by > the global root. > Others might argue that containers are not a full virtual Linux with > all features and > an administrator may want to collect cores from all containers. I agree there are some value in the admin getting a notification if they choose to. The problem is that there is no clean mechanism for the admin to send the core dump back to the namespace of the process. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
