When working with Linux systems, particularly in containerized environments, knowing how to inspect the cgroup (control group) of a process is crucial for resource management and debugging. Here are several reliable methods to achieve this.

The most straightforward way to check a process's cgroup is through the proc filesystem:

cat /proc/[PID]/cgroup

Example output:

12:memory:/docker/abcdef123456
6:cpuacct,cpu:/docker/abcdef123456
3:blkio:/docker/abcdef123456

Modern versions of ps (from procps-ng 3.3.0+) support cgroup information:

ps -o cgroup [PID]

Or for more detailed output:

ps xawf -eo pid,user,cgroup,args

For systems using systemd, you can inspect the hierarchy:

systemd-cgls

To find a specific process:

systemd-cgls | grep [PID]

On systems using cgroup v2:

cat /sys/fs/cgroup/[PID]/cgroup.procs

Or to find all processes in a cgroup:

cat /sys/fs/cgroup/unified/cgroup.procs

When debugging a containerized application:

# Find container process
docker ps
docker top [CONTAINER_ID]

# Then check its cgroup
cat /proc/$(docker inspect --format '{{.State.Pid}}' [CONTAINER_ID])/cgroup

Here's a bash function to quickly check cgroups:

get_cgroup() {
  if [ -z "$1" ]; then
    echo "Usage: get_cgroup [PID]"
    return 1
  fi
  echo "Cgroup information for PID $1:"
  cat "/proc/$1/cgroup"
}

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When working with Linux process management, you'll often need to inspect which control groups (cgroups) a particular process belongs to. This information becomes crucial for resource monitoring, container orchestration, and system debugging.

The most straightforward method is to examine the process's entry in the /proc filesystem:

cat /proc/[PID]/cgroup

For example, to check cgroups for process ID 1234:

cat /proc/1234/cgroup

On systems using systemd (most modern distributions), you can use:

systemd-cgls [PID]

Or to see the full hierarchy:

systemd-cgtop

Several other tools can provide this information:

ps xawf -eo pid,user,cgroup,args
lscgroup -a
cgclassify --list

Here's a bash function to display detailed cgroup information:

function show_cgroups() {
    local pid=$1
    echo "Cgroup information for PID $pid:"
    echo "--------------------------------"
    cat /proc/$pid/cgroup
    echo
    echo "Memory cgroup details:"
    cat /sys/fs/cgroup/memory/$(cat /proc/$pid/cgroup | grep memory | cut -d: -f3)/tasks | grep -w $pid
}

A typical output looks like:

12:memory:/user.slice/user-1000.slice/session-1.scope
11:devices:/user.slice
10:net_cls,net_prio:/
9:perf_event:/
8:pids:/user.slice/user-1000.slice/session-1.scope

Each line shows the cgroup hierarchy ID, controller type, and path within the cgroup filesystem.

For containerized processes, you might use:

docker inspect --format '{{.State.Pid}}' container_name | xargs -I {} cat /proc/{}/cgroup