# Identify Process Cgroup by PID

## TL;DR

You can identify a process's cgroup by reading `/proc/<PID>/cgroup`.

## Outcome

Multiple methods to find which cgroup a process belongs to using its PID.

## Conversation

**Question:** Can I identify the process's cgroup by having its PID?

**Answer:** Yes, here are the main methods:

### Method 1: Read `/proc/<PID>/cgroup`

```bash
cat /proc/<PID>/cgroup
```

This shows all cgroup controllers the process belongs to. For example:
```
12:blkio:/user.slice
11:memory:/user.slice/user-1000.slice
...
0::/user.slice/user-1000.slice/session-1.scope
```

### Method 2: Using `ps` with format options

```bash
ps -o pid,cgroup -p <PID>
```

### Method 3: Using `systemd-cgls`

If you're on a systemd system:
```bash
systemd-cgls --unit <unit-name>
# or to see the whole tree
systemd-cgls
```

### Method 4: Check cgroup v2 unified hierarchy

On cgroup v2 systems, check:
```bash
cat /proc/<PID>/cgroup
# Output will look like: 0::/user.slice/user-1000.slice/session-1.scope
```

The path after `::` is the cgroup path under `/sys/fs/cgroup/`.

### Quick one-liner

```bash
cat /proc/self/cgroup  # For current shell
cat /proc/$$/cgroup    # Also current shell
cat /proc/1234/cgroup  # For PID 1234
```