Finding Docker container processes? (from host point of view) - linux

Question

I am doing some tests on docker and containers and I was wondering:
Is there a method I can use to find all process associated with a docker container by its name or ID from the host point of view.
After all, at the end of the day a container is a set of virtualized processes.

Answer 1

You can use docker top command.
This command lists all processes running within your container.
For instance this command on a single process container on my box displays:
UID PID PPID C STIME TTY TIME CMD
root 14097 13930 0 23:17 pts/6 00:00:00 /bin/bash
All methods mentioned by others are also possible to use but this one should be easiest.
Update:
To simply get the main process id within the container use this command:
docker inspect -f '{{.State.Pid}}' <container id>

Answer 2

Another way to get an overview of all Docker processes running on a host is using generic cgroup based systemd tools.
systemd-cgls will show all our cgroups and the processes running in them in a tree-view, like this:
├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 21
├─docker
│ ├─070a034d27ed7a0ac0d336d72cc14671584cc05a4b6802b4c06d4051ce3213bd
│ │ └─14043 bash
│ ├─dd952fc28077af16a2a0a6a3231560f76f363359f061c797b5299ad8e2614245
│ │ └─3050 go-cron -s 0 0 * * * * -- automysqlbackup
As every Docker container has its own cgroup, you can also see Docker Containers and their corresponding host processes this way.
Two interesting properties of this method:
It works even if the Docker Daemon(s) are defunct.
It's a pretty quick overview.
You can also use systemd-cgtop to get an overview of the resource usage of Docker Containers, similar to top.
By the way: Since systemd services also correspond to cgroups these methods are also applicable to non-Dockerized systemd services.

Answer 3

I found a similar solution using a bash script in one line:
for i in $(docker container ls --format "{{.ID}}"); do docker inspect -f '{{.State.Pid}} {{.Name}}' $i; done

Answer 4

the process run in a docker container is a child of a process named containerd-shim (in Docker v18.09.4)
First figure out the process IDs of the containerd-shim processes.
For each of them, find their child process.
pgrep containerd-shim
7105
7141
7248
To find the child process of parent process 7105:
pgrep -P 7105
7127
In the end you could get the list with:
for i in $(pgrep containerd-shim); do pgrep -P $i; done
7127
7166
7275

Answer 5

When running this on the host, it will give you a list of processes running in a container with <Container ID>, showing host PIDs instead of container PIDs.
DID=$(docker inspect -f '{{.State.Pid}}' <Container ID>);ps --ppid $DID -o pid,ppid,cmd

Answer 6

docker ps will list docker containers that are running.
docker exec <id|name> ps will tell you the processes it's running.

Answer 7

Since the following command shows only the container's itself process ID (not all child processes):
docker inspect -f '{{.State.Pid}}' <container-name_or_ID>
To find a process that is the child of a container, this process ID must be find in directory /proc. So find "processID" inside it and then find the container hash from file:
/proc/parent_process/task/processID
and then cut container ID from hash (first 12-digits of the container hash) and then find the container itself:
#!/bin/bash
processPath=$(find /proc/ -name $1 2>/dev/null)
containerID=$(cat ${processPath}/cgroup | fgrep 'pids:/docker/' | sed -e 's#.*/docker/##g' | cut -c 1-12)
docker ps | fgrep $containerID
Save above script in a file such as: p2c and run it by:
p2c <PID>
For example:
p2c 85888

Answer 8

Another solution with docker container and docker top
docker ps --format "{{.ID}}" | xargs -I'{}' docker top {} -o pid | awk '!/PID/'
Note: awk '!/PID/' just remove the PID header from the output of docker top
If you want to know the whole process tree of docker container, you can try it
docker ps --format "{{.ID}}" | xargs -I'{}' docker top {} -o pid | awk '!/PID/' | xargs -I'{}' pstree -psa {}

Answer 9

Docker stats "container id"
Shows the resource consumption along with pid or simply Docker ps .
Probably this cheat sheet can be of use.
http://theearlybirdtechnology.com/2017/08/12/docker-cheatsheet/