3:17 p.m.
Given an alpine:3.10.1 image
```
podman pull alpine:3.10.1
```
And a unit file foo.service
```
[Service]
ExecStart=/usr/bin/podman run --name %N --rm --tty alpine:3.10.1 sleep 99999
ExecStop=/usr/bin/podman stop %N
```
And starting `foo.service` with `systemctl`
```
# systemctl daemon-reload
# systemctl start foo.service
```
I don't see my `sleep` process in `foo.service` status:
```
# systemctl status foo.service | head
● foo.service
Loaded: loaded (/etc/systemd/system/foo.service; static; vendor
preset: enabled)
Active: active (running) since Sat 2019-08-10 19:58:05 UTC; 40s ago
Main PID: 15524 (podman)
Tasks: 9
Memory: 7.3M
CPU: 79ms
CGroup: /system.slice/foo.service
└─15524 /usr/bin/podman run --name foo --rm --tty
alpine:3.10.1 sleep 99999
```
I see `conmon` land in a different cgroup, visible with the
`systemd-cgls` command:
```
# systemd-cgls
Control group /:
-.slice
├─init.scope
│ └─1 /sbin/init
├─machine.slice
│ ├─libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a
│ │ └─15648 /usr/bin/conmon -s -c
c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0
│ └─libpod-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
│ └─15662 sleep 99999
├─system.slice
│ ├─mdadm.service
│ │ └─880 /sbin/mdadm --monitor --pid-file /run/mdadm/monitor.pid
--daemonise --s
│ ├─foo.service
│ │ └─15524 /usr/bin/podman run --name foo --rm --tty alpine:3.10.1 sleep 99999
```
From listening to youtube presentations about podman I thought podman
using a traditional fork exec model would imply all my processes would
show up in the same `systemctl status` and be in the same control
group controlled by systemd.
Looking at the output of `ps` also shows that the `sleep` process is
the parent of the `conmon` process and not the `podman` process:
```
# ps -Heo pid,ppid,comm,cgroup
15524 1 podman
11:memory:/system.slice/foo.service,8:pids:/system.sl
15648 1 conmon
11:memory:/machine.slice/libpod-conmon-c598f5a0c84881
15662 15648 sleep
11:memory:/machine.slice/libpod-c598f5a0c84881c69dcd6
```
Instead it looks like `conmon` in a `scope` unit named:
```
libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
```
Why doesn't `conmon` and `sleep` land in the same `foo.service` systemd unit?
9:01 a.m.
New subject: Why does conmon land in a different cgroup when using systemd and podman?
On 2019-08-10 13:17, Max Bigras wrote:
Given an alpine:3.10.1 image
```
podman pull alpine:3.10.1
```
And a unit file foo.service
```
[Service]
ExecStart=/usr/bin/podman run --name %N --rm --tty alpine:3.10.1 sleep 99999
ExecStop=/usr/bin/podman stop %N
```
And starting `foo.service` with `systemctl`
```
# systemctl daemon-reload
# systemctl start foo.service
```
I don't see my `sleep` process in `foo.service` status:
```
# systemctl status foo.service | head
● foo.service
Loaded: loaded (/etc/systemd/system/foo.service; static; vendor
preset: enabled)
Active: active (running) since Sat 2019-08-10 19:58:05 UTC; 40s ago
Main PID: 15524 (podman)
Tasks: 9
Memory: 7.3M
CPU: 79ms
CGroup: /system.slice/foo.service
└─15524 /usr/bin/podman run --name foo --rm --tty
alpine:3.10.1 sleep 99999
```
I see `conmon` land in a different cgroup, visible with the
`systemd-cgls` command:
```
# systemd-cgls
Control group /:
-.slice
├─init.scope
│ └─1 /sbin/init
├─machine.slice
│ ├─libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a
│ │ └─15648 /usr/bin/conmon -s -c
c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0
│ └─libpod-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
│ └─15662 sleep 99999
├─system.slice
│ ├─mdadm.service
│ │ └─880 /sbin/mdadm --monitor --pid-file /run/mdadm/monitor.pid
--daemonise --s
│ ├─foo.service
│ │ └─15524 /usr/bin/podman run --name foo --rm --tty alpine:3.10.1 sleep 99999
```
From listening to youtube presentations about podman I thought podman
using a traditional fork exec model would imply all my processes would
show up in the same `systemctl status` and be in the same control
group controlled by systemd.
Looking at the output of `ps` also shows that the `sleep` process is
the parent of the `conmon` process and not the `podman` process:
```
# ps -Heo pid,ppid,comm,cgroup
15524 1 podman
11:memory:/system.slice/foo.service,8:pids:/system.sl
15648 1 conmon
11:memory:/machine.slice/libpod-conmon-c598f5a0c84881
15662 15648 sleep
11:memory:/machine.slice/libpod-c598f5a0c84881c69dcd6
```
Instead it looks like `conmon` in a `scope` unit named:
```
libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
```
Why doesn't `conmon` and `sleep` land in the same `foo.service` systemd unit?
_______________________________________________
Podman mailing list -- podman(a)lists.podman.io
To unsubscribe send an email to podman-leave(a)lists.podman.io
All Linux containers, at present, will create and manage their own
CGroups, independent of systemd (with a few potential exceptions).
This is mostly done so they can independently manage resources, though
it is also necessary to do some common container operations - the
'podman stats' and 'podman top' commands, for example, track processes
in the container by its CGroup.
The exception I mentioned was rootless containers in a CGroup v1
environment. There is no support for delegation to rootless containers
in the V1 hierarchy, so the containers have no permission to create
CGroups.
For most people, this is perfectly sufficient, but we definitely
recognize that there are use cases that require keeping containers in
CGroups managed elsewhere - most notably, from systemd unit files.
There is work ongoing at [1] to enable this, though I caution that
there are a lot of moving parts here - we don't just need support in
Podman, but also in 'runc' - Podman isn't actually creating the new
CGroup for the container, the OCI runtime (usually 'runc') is.
Also, a bit more context: the Conmon CGroup is not the container
CGroup. Conmon creates its own CGroup (for various legacy reasons -
we're evaluating whether these still hold true, and this could change)
and then spawns the OCI runtime - and then the OCI runtime spawns its
own CGroup. So you'll have a Conmon CGroup and another for the actual
container (the two 'libpod' cgroups).
The parent situation is simpler to explain; Podman launches conmon,
and then conmon double-forks to daemonize. At that point, the two are
effectively separate; Podman itself can go away completely, and the
Conmon process will continue managing the container. This is
deliberate - Podman is just the frontend that launches the container,
and we don't need it to keep running once the container is started.
Because of this, we recommend tracking Conmon, not Podman, with unit
files. In Podman 1.5.0 and later, 'podman generate systemd' will
properly handle this, creating a unit file that tracks Conmon using
PID file.
I hope this helps explain things.
Thanks,
Matt Heon
[1] https://github.com/containers/libpod/pull/3581
12:56 p.m.
New subject: Why does conmon land in a different cgroup when using systemd and podman?
Thank you for the explanation and link to WIP PR #3581 [1]!
After reading your explanation and answers to my question on Stack
Exchange [2] I'm learning more about what's going on.
Also, a bit more context: the Conmon CGroup is not the container
CGroup. Conmon creates its own CGroup (for various legacy reasons -
we're evaluating whether these still hold true, and this could change)
and then spawns the OCI runtime - and then the OCI runtime spawns its
own CGroup. So you'll have a Conmon CGroup and another for the actual
container (the two 'libpod' cgroups).
I made an example illustrating the three cgroups you mentioned:
1. /system.slice/example.service for my systemd service
2. /machine.slice/libpod-conmon-a75a16081e23b...scope for conmon
3. /machine.slice/libpod-a75a16081e23bb03589....scope for processes
inside the container (sleep in this case)
```
# podman create --name example --tty alpine sleep 9999
# cat <<'EOF' > /etc/systemd/system/example.service
[Service]
ExecStart=/usr/bin/podman start --attach %N
ExecStop=/usr/bin/podman stop %N
EOF
# systemctl daemon-reload
# systemd-cgls /machine.slice
Control group /machine.slice
# systemctl start example
# systemd-cgls /machine.slice
Control group /machine.slice:
├─libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297
│ └─22385 /usr/bin/conmon -s -c a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7
└─libpod-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
└─22399 sleep 9999
# systemd-cgls /system.slice/example.service
Control group /system.slice/example.service:
└─22308 /usr/bin/podman start --attach example
```
From listening to a presentation from Lennart on YouTube systemd and
Control Groups [3], I learned that the scope unit is just like the
service unit because it manages processes; however, the scope unit is
different from the service unit because scope units can be dynamically
generated. In this case that explanation matches with what we're
seeing here: two scope units for conmon and sleep and dynamically
generated.
Because of this, we recommend tracking Conmon, not Podman, with unit
files. In Podman 1.5.0 and later, 'podman generate systemd' will
properly handle this, creating a unit file that tracks Conmon using
PID file.
Can you illustrate an example of using systemd to track conmon instead
of podman?
My goal is to have one way to stop, start, and enable my containers.
In the example above I know I can check the status of the conmon scope
unit, it looks like the name comes from the container id:
```
# systemctl status
libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
● libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297
Loaded: loaded
Transient: yes
Drop-In: /run/systemd/system/libpod-conmon-a75a16081e23bb03589b214580b3226d8b2
└─50-DefaultDependencies.conf, 50-Delegate.conf, 50-Slice.conf
Active: active (running) since Mon 2019-08-12 17:20:17 UTC; 2min 20s ago
Tasks: 2
Memory: 200.0K
CPU: 17ms
CGroup: /machine.slice/libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a
└─22631 /usr/bin/conmon -s -c a75a16081e23bb03589b214580b3226d8b2ef77
Aug 12 17:20:17 srv0 systemd[1]: Started libpod-conmon-a75a16081e23bb03589b21458
# podman ps
CONTAINER ID IMAGE COMMAND CREATED
STATUS PORTS NAMES
a75a16081e23 docker.io/library/alpine:latest sleep 9999 41 minutes
ago Up 22 minutes ago example
# systemctl show
libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
| grep ExecStart
```
I didn't see an ExecStart directive inside the scope unit.
podman generate systemd
Ah, I see what you mean
```
# podman generate systemd example > /etc/systemd/system/example.service
# systemctl daemon-reload
# systemctl cat example
[Unit]
Description=a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297 Pod
[Service]
Restart=on-failure
ExecStart=/usr/bin/podman start a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7
ExecStop=/usr/bin/podman stop -t 10 a75a16081e23bb03589b214580b3226d8b2ef77a382c
KillMode=none
Type=forking
PIDFile=/var/lib/containers/storage/overlay-containers/a75a16081e23bb03589b21458
[Install]
WantedBy=multi-user.target
# systemctl start example
# journalctl -u example | grep PID | tail -n 1
Aug 12 17:50:38 srv0 systemd[1]: example.service: PID file
/var/lib/containers/storage/overlay-containers/a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297/userdata/a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.pid
not readable (yet?) after start: No such file or directory
```
Is using `podman generate systemd example` planned for the future or
is it supposed to work now?
[1] https://github.com/containers/libpod/pull/3581
[2]
https://unix.stackexchange.com/questions/534843/why-is-conmon-in-a-differ...
[3] https://youtu.be/7CWmuhkgZWs?t=2204
On Mon, Aug 12, 2019 at 7:01 AM Matt Heon <mheon(a)redhat.com> wrote:
>
> On 2019-08-10 13:17, Max Bigras wrote:
> >Given an alpine:3.10.1 image
> >
> >```
> >podman pull alpine:3.10.1
> >```
> >
> >And a unit file foo.service
> >
> >```
> >[Service]
> >ExecStart=/usr/bin/podman run --name %N --rm --tty alpine:3.10.1 sleep 99999
> >ExecStop=/usr/bin/podman stop %N
> >```
> >
> >And starting `foo.service` with `systemctl`
> >
> >```
> ># systemctl daemon-reload
> ># systemctl start foo.service
> >```
> >
> >I don't see my `sleep` process in `foo.service` status:
> >
> >```
> ># systemctl status foo.service | head
> >● foo.service
> > Loaded: loaded (/etc/systemd/system/foo.service; static; vendor
> >preset: enabled)
> > Active: active (running) since Sat 2019-08-10 19:58:05 UTC; 40s ago
> > Main PID: 15524 (podman)
> > Tasks: 9
> > Memory: 7.3M
> > CPU: 79ms
> > CGroup: /system.slice/foo.service
> > └─15524 /usr/bin/podman run --name foo --rm --tty
> >alpine:3.10.1 sleep 99999
> >```
> >
> >I see `conmon` land in a different cgroup, visible with the
> >`systemd-cgls` command:
> >
> >```
> ># systemd-cgls
> >Control group /:
> >-.slice
> >├─init.scope
> >│ └─1 /sbin/init
> >├─machine.slice
> >│
├─libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a
> >│ │ └─15648 /usr/bin/conmon -s -c
> >c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0
> >│
└─libpod-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
> >│ └─15662 sleep 99999
> >├─system.slice
> >│ ├─mdadm.service
> >│ │ └─880 /sbin/mdadm --monitor --pid-file /run/mdadm/monitor.pid
> >--daemonise --s
> >│ ├─foo.service
> >│ │ └─15524 /usr/bin/podman run --name foo --rm --tty alpine:3.10.1 sleep 99999
> >```
> >
> >From listening to youtube presentations about podman I thought podman
> >using a traditional fork exec model would imply all my processes would
> >show up in the same `systemctl status` and be in the same control
> >group controlled by systemd.
> >
> >Looking at the output of `ps` also shows that the `sleep` process is
> >the parent of the `conmon` process and not the `podman` process:
> >
> >```
> ># ps -Heo pid,ppid,comm,cgroup
> >15524 1 podman
> >11:memory:/system.slice/foo.service,8:pids:/system.sl
> >15648 1 conmon
> >11:memory:/machine.slice/libpod-conmon-c598f5a0c84881
> >15662 15648 sleep
> >11:memory:/machine.slice/libpod-c598f5a0c84881c69dcd6
> >```
> >
> >Instead it looks like `conmon` in a `scope` unit named:
> >
> >```
>
>libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
> >```
> >
> >Why doesn't `conmon` and `sleep` land in the same `foo.service` systemd
unit?
> >_______________________________________________
> >Podman mailing list -- podman(a)lists.podman.io
> >To unsubscribe send an email to podman-leave(a)lists.podman.io
>
> All Linux containers, at present, will create and manage their own
> CGroups, independent of systemd (with a few potential exceptions).
> This is mostly done so they can independently manage resources, though
> it is also necessary to do some common container operations - the
> 'podman stats' and 'podman top' commands, for example, track
processes
> in the container by its CGroup.
>
> The exception I mentioned was rootless containers in a CGroup v1
> environment. There is no support for delegation to rootless containers
> in the V1 hierarchy, so the containers have no permission to create
> CGroups.
>
> For most people, this is perfectly sufficient, but we definitely
> recognize that there are use cases that require keeping containers in
> CGroups managed elsewhere - most notably, from systemd unit files.
> There is work ongoing at [1] to enable this, though I caution that
> there are a lot of moving parts here - we don't just need support in
> Podman, but also in 'runc' - Podman isn't actually creating the new
> CGroup for the container, the OCI runtime (usually 'runc') is.
>
> Also, a bit more context: the Conmon CGroup is not the container
> CGroup. Conmon creates its own CGroup (for various legacy reasons -
> we're evaluating whether these still hold true, and this could change)
> and then spawns the OCI runtime - and then the OCI runtime spawns its
> own CGroup. So you'll have a Conmon CGroup and another for the actual
> container (the two 'libpod' cgroups).
>
> The parent situation is simpler to explain; Podman launches conmon,
> and then conmon double-forks to daemonize. At that point, the two are
> effectively separate; Podman itself can go away completely, and the
> Conmon process will continue managing the container. This is
> deliberate - Podman is just the frontend that launches the container,
> and we don't need it to keep running once the container is started.
>
> Because of this, we recommend tracking Conmon, not Podman, with unit
> files. In Podman 1.5.0 and later, 'podman generate systemd' will
> properly handle this, creating a unit file that tracks Conmon using
> PID file.
>
> I hope this helps explain things.
>
> Thanks,
> Matt Heon
>
> [1] https://github.com/containers/libpod/pull/3581
1:20 p.m.
New subject: Why does conmon land in a different cgroup when using systemd and podman?
On 2019-08-12 10:56, Max Bigras wrote:
Thank you for the explanation and link to WIP PR #3581 [1]!
After reading your explanation and answers to my question on Stack
Exchange [2] I'm learning more about what's going on.
>Also, a bit more context: the Conmon CGroup is not the container
>CGroup. Conmon creates its own CGroup (for various legacy reasons -
>we're evaluating whether these still hold true, and this could change)
>and then spawns the OCI runtime - and then the OCI runtime spawns its
>own CGroup. So you'll have a Conmon CGroup and another for the actual
>container (the two 'libpod' cgroups).
I made an example illustrating the three cgroups you mentioned:
1. /system.slice/example.service for my systemd service
2. /machine.slice/libpod-conmon-a75a16081e23b...scope for conmon
3. /machine.slice/libpod-a75a16081e23bb03589....scope for processes
inside the container (sleep in this case)
```
# podman create --name example --tty alpine sleep 9999
# cat <<'EOF' > /etc/systemd/system/example.service
[Service]
ExecStart=/usr/bin/podman start --attach %N
ExecStop=/usr/bin/podman stop %N
EOF
# systemctl daemon-reload
# systemd-cgls /machine.slice
Control group /machine.slice
# systemctl start example
# systemd-cgls /machine.slice
Control group /machine.slice:
├─libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297
│ └─22385 /usr/bin/conmon -s -c a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7
└─libpod-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
└─22399 sleep 9999
# systemd-cgls /system.slice/example.service
Control group /system.slice/example.service:
└─22308 /usr/bin/podman start --attach example
```
From listening to a presentation from Lennart on YouTube systemd and
Control Groups [3], I learned that the scope unit is just like the
service unit because it manages processes; however, the scope unit is
different from the service unit because scope units can be dynamically
generated. In this case that explanation matches with what we're
seeing here: two scope units for conmon and sleep and dynamically
generated.
>Because of this, we recommend tracking Conmon, not Podman, with unit
>files. In Podman 1.5.0 and later, 'podman generate systemd' will
>properly handle this, creating a unit file that tracks Conmon using
>PID file.
Can you illustrate an example of using systemd to track conmon instead
of podman?
The unit file generated by `generate systemd` below is a good example
of what we want to use - in contrast to using a `Type=simple` unit
file using `podman start --attach` (which was previously recommended).
As previously mentioned, Podman becomes effectively independent of the
container when it's running - so the Podman process can disappear but
the container may still be running, which is not conducive to the
Type=simple unit.
My goal is to have one way to stop, start, and enable my containers.
In the example above I know I can check the status of the conmon scope
unit, it looks like the name comes from the container id:
```
# systemctl status
libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
● libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297
Loaded: loaded
Transient: yes
Drop-In: /run/systemd/system/libpod-conmon-a75a16081e23bb03589b214580b3226d8b2
└─50-DefaultDependencies.conf, 50-Delegate.conf, 50-Slice.conf
Active: active (running) since Mon 2019-08-12 17:20:17 UTC; 2min 20s ago
Tasks: 2
Memory: 200.0K
CPU: 17ms
CGroup: /machine.slice/libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a
└─22631 /usr/bin/conmon -s -c a75a16081e23bb03589b214580b3226d8b2ef77
Aug 12 17:20:17 srv0 systemd[1]: Started libpod-conmon-a75a16081e23bb03589b21458
# podman ps
CONTAINER ID IMAGE COMMAND CREATED
STATUS PORTS NAMES
a75a16081e23 docker.io/library/alpine:latest sleep 9999 41 minutes
ago Up 22 minutes ago example
# systemctl show
libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
| grep ExecStart
```
I didn't see an ExecStart directive inside the scope unit.
>podman generate systemd
Ah, I see what you mean
```
# podman generate systemd example > /etc/systemd/system/example.service
# systemctl daemon-reload
# systemctl cat example
[Unit]
Description=a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297 Pod
[Service]
Restart=on-failure
ExecStart=/usr/bin/podman start a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7
ExecStop=/usr/bin/podman stop -t 10 a75a16081e23bb03589b214580b3226d8b2ef77a382c
KillMode=none
Type=forking
PIDFile=/var/lib/containers/storage/overlay-containers/a75a16081e23bb03589b21458
[Install]
WantedBy=multi-user.target
# systemctl start example
# journalctl -u example | grep PID | tail -n 1
Aug 12 17:50:38 srv0 systemd[1]: example.service: PID file
/var/lib/containers/storage/overlay-containers/a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297/userdata/a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.pid
not readable (yet?) after start: No such file or directory
```
Is using `podman generate systemd example` planned for the future or
is it supposed to work now?
It's bugged in 1.4.x - fixed in 1.5.0 (just released Friday).
[1] https://github.com/containers/libpod/pull/3581
[2]
https://unix.stackexchange.com/questions/534843/why-is-conmon-in-a-differ...
[3] https://youtu.be/7CWmuhkgZWs?t=2204
On Mon, Aug 12, 2019 at 7:01 AM Matt Heon <mheon(a)redhat.com> wrote:
>
> On 2019-08-10 13:17, Max Bigras wrote:
> >Given an alpine:3.10.1 image
> >
> >```
> >podman pull alpine:3.10.1
> >```
> >
> >And a unit file foo.service
> >
> >```
> >[Service]
> >ExecStart=/usr/bin/podman run --name %N --rm --tty alpine:3.10.1 sleep 99999
> >ExecStop=/usr/bin/podman stop %N
> >```
> >
> >And starting `foo.service` with `systemctl`
> >
> >```
> ># systemctl daemon-reload
> ># systemctl start foo.service
> >```
> >
> >I don't see my `sleep` process in `foo.service` status:
> >
> >```
> ># systemctl status foo.service | head
> >● foo.service
> > Loaded: loaded (/etc/systemd/system/foo.service; static; vendor
> >preset: enabled)
> > Active: active (running) since Sat 2019-08-10 19:58:05 UTC; 40s ago
> > Main PID: 15524 (podman)
> > Tasks: 9
> > Memory: 7.3M
> > CPU: 79ms
> > CGroup: /system.slice/foo.service
> > └─15524 /usr/bin/podman run --name foo --rm --tty
> >alpine:3.10.1 sleep 99999
> >```
> >
> >I see `conmon` land in a different cgroup, visible with the
> >`systemd-cgls` command:
> >
> >```
> ># systemd-cgls
> >Control group /:
> >-.slice
> >├─init.scope
> >│ └─1 /sbin/init
> >├─machine.slice
> >│
├─libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a
> >│ │ └─15648 /usr/bin/conmon -s -c
> >c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0
> >│
└─libpod-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
> >│ └─15662 sleep 99999
> >├─system.slice
> >│ ├─mdadm.service
> >│ │ └─880 /sbin/mdadm --monitor --pid-file /run/mdadm/monitor.pid
> >--daemonise --s
> >│ ├─foo.service
> >│ │ └─15524 /usr/bin/podman run --name foo --rm --tty alpine:3.10.1 sleep 99999
> >```
> >
> >From listening to youtube presentations about podman I thought podman
> >using a traditional fork exec model would imply all my processes would
> >show up in the same `systemctl status` and be in the same control
> >group controlled by systemd.
> >
> >Looking at the output of `ps` also shows that the `sleep` process is
> >the parent of the `conmon` process and not the `podman` process:
> >
> >```
> ># ps -Heo pid,ppid,comm,cgroup
> >15524 1 podman
> >11:memory:/system.slice/foo.service,8:pids:/system.sl
> >15648 1 conmon
> >11:memory:/machine.slice/libpod-conmon-c598f5a0c84881
> >15662 15648 sleep
> >11:memory:/machine.slice/libpod-c598f5a0c84881c69dcd6
> >```
> >
> >Instead it looks like `conmon` in a `scope` unit named:
> >
> >```
>
>libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
> >```
> >
> >Why doesn't `conmon` and `sleep` land in the same `foo.service` systemd
unit?
> >_______________________________________________
> >Podman mailing list -- podman(a)lists.podman.io
> >To unsubscribe send an email to podman-leave(a)lists.podman.io
>
> All Linux containers, at present, will create and manage their own
> CGroups, independent of systemd (with a few potential exceptions).
> This is mostly done so they can independently manage resources, though
> it is also necessary to do some common container operations - the
> 'podman stats' and 'podman top' commands, for example, track
processes
> in the container by its CGroup.
>
> The exception I mentioned was rootless containers in a CGroup v1
> environment. There is no support for delegation to rootless containers
> in the V1 hierarchy, so the containers have no permission to create
> CGroups.
>
> For most people, this is perfectly sufficient, but we definitely
> recognize that there are use cases that require keeping containers in
> CGroups managed elsewhere - most notably, from systemd unit files.
> There is work ongoing at [1] to enable this, though I caution that
> there are a lot of moving parts here - we don't just need support in
> Podman, but also in 'runc' - Podman isn't actually creating the new
> CGroup for the container, the OCI runtime (usually 'runc') is.
>
> Also, a bit more context: the Conmon CGroup is not the container
> CGroup. Conmon creates its own CGroup (for various legacy reasons -
> we're evaluating whether these still hold true, and this could change)
> and then spawns the OCI runtime - and then the OCI runtime spawns its
> own CGroup. So you'll have a Conmon CGroup and another for the actual
> container (the two 'libpod' cgroups).
>
> The parent situation is simpler to explain; Podman launches conmon,
> and then conmon double-forks to daemonize. At that point, the two are
> effectively separate; Podman itself can go away completely, and the
> Conmon process will continue managing the container. This is
> deliberate - Podman is just the frontend that launches the container,
> and we don't need it to keep running once the container is started.
>
> Because of this, we recommend tracking Conmon, not Podman, with unit
> files. In Podman 1.5.0 and later, 'podman generate systemd' will
> properly handle this, creating a unit file that tracks Conmon using
> PID file.
>
> I hope this helps explain things.
>
> Thanks,
> Matt Heon
>
> [1] https://github.com/containers/libpod/pull/3581
2:06 p.m.
New subject: Why does conmon land in a different cgroup when using systemd and podman?
It's bugged in 1.4.x - fixed in 1.5.0 (just released Friday).
Right on! I just installed a fresh podman package on Ubuntu 16.04 and
got version 1.5.0.
I made an example using the `--conmon-pidfile` flag to podman create.
I never made a custom pid file before so I'm searched around, it looks
like people write pid files to /var/run/foo.pid.
```
# podman create \
--name bar \
--tty \
--conmon-pidfile /var/run/bar.pid \
alpine \
/bin/sh -c 'while true; do date; sleep 1; done'
33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496
# podman generate systemd bar > /etc/systemd/system/bar.service
# systemctl daemon-reload
# systemctl start bar
# systemctl status bar
● bar.service - 33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496
Loaded: loaded (/etc/systemd/system/bar.service; disabled; vendor preset: ena
Active: active (running) since Mon 2019-08-12 18:53:22 UTC; 31s ago
Process: 15832 ExecStart=/usr/bin/podman start 33b7486fda2846ae780cef4913c3a46
Main PID: 15951 (conmon)
Tasks: 0
Memory: 364.0K
CPU: 71ms
CGroup: /system.slice/bar.service
‣ 15951 /usr/bin/conmon --api-version 1 -s -c 33b7486fda2846ae780cef4
Aug 12 18:53:22 srv0 systemd[1]: Starting 33b7486fda2846ae780cef4913c3a46be6005e
Aug 12 18:53:22 srv0 podman[15832]: 2019-08-12 18:53:22.43628578 +0000 UTC m=+0.
Aug 12 18:53:22 srv0 podman[15832]: 2019-08-12 18:53:22.443460842 +0000 UTC m=+0
Aug 12 18:53:22 srv0 podman[15832]: 33b7486fda2846ae780cef4913c3a46be6005e6bb75c
Aug 12 18:53:22 srv0 systemd[1]: Started 33b7486fda2846ae780cef4913c3a46be6005e6
# podman ps | grep bar
33b7486fda28 docker.io/library/alpine:latest /bin/sh -c while ...
40 seconds ago Up 18 seconds ago bar
# systemd-cgls /system.slice/bar.service
Control group /system.slice/bar.service:
# systemd-cgls /machine.slice
Control group /machine.slice:
├─libpod-33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496.scope
│ ├─15966 /bin/sh -c while true; do date; sleep 1; done
│ └─16234 sleep 1
└─libpod-conmon-33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496
└─15951 /usr/bin/conmon --api-version 1 -s -c 33b7486fda2846ae780cef4913c3a46b
```
`systemctl status` reports the conmon process is in the
/system.slice/bar.service cgroup but I'm not seeing the
/system.slice/bar.service cgroup in the output of `systemd-cgls`. And
instead only seeing the two new cgroups for the scope units in
/machine.slice
```
root@srv0:~# systemd-cgls /system.slice/bar.service
Control group /system.slice/bar.service:
root@srv0:~# systemd-cgls /machine.slice
Control group /machine.slice:
├─libpod-33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496.scope
│ ├─15966 /bin/sh -c while true; do date; sleep 1; done
│ └─16979 sleep 1
└─libpod-conmon-33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496
└─15951 /usr/bin/conmon --api-version 1 -s -c 33b7486fda2846ae780cef4913c3a46b
```
Is `systemctl status` showing a CGroup that doesn't exist unexpected?
On Mon, Aug 12, 2019 at 11:20 AM Matt Heon <mheon(a)redhat.com> wrote:
>
> On 2019-08-12 10:56, Max Bigras wrote:
> >Thank you for the explanation and link to WIP PR #3581 [1]!
> >After reading your explanation and answers to my question on Stack
> >Exchange [2] I'm learning more about what's going on.
> >
> >>Also, a bit more context: the Conmon CGroup is not the container
> >>CGroup. Conmon creates its own CGroup (for various legacy reasons -
> >>we're evaluating whether these still hold true, and this could change)
> >>and then spawns the OCI runtime - and then the OCI runtime spawns its
> >>own CGroup. So you'll have a Conmon CGroup and another for the actual
> >>container (the two 'libpod' cgroups).
> >
> >I made an example illustrating the three cgroups you mentioned:
> >
> >1. /system.slice/example.service for my systemd service
> >2. /machine.slice/libpod-conmon-a75a16081e23b...scope for conmon
> >3. /machine.slice/libpod-a75a16081e23bb03589....scope for processes
> >inside the container (sleep in this case)
> >
> >```
> ># podman create --name example --tty alpine sleep 9999
> ># cat <<'EOF' > /etc/systemd/system/example.service
> >[Service]
> >ExecStart=/usr/bin/podman start --attach %N
> >ExecStop=/usr/bin/podman stop %N
> >EOF
> ># systemctl daemon-reload
> ># systemd-cgls /machine.slice
> >Control group /machine.slice
> ># systemctl start example
> ># systemd-cgls /machine.slice
> >Control group /machine.slice:
> >├─libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297
> >│ └─22385 /usr/bin/conmon -s -c a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7
> >└─libpod-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
> > └─22399 sleep 9999
> ># systemd-cgls /system.slice/example.service
> >Control group /system.slice/example.service:
> >└─22308 /usr/bin/podman start --attach example
> >```
> >
> >From listening to a presentation from Lennart on YouTube systemd and
> >Control Groups [3], I learned that the scope unit is just like the
> >service unit because it manages processes; however, the scope unit is
> >different from the service unit because scope units can be dynamically
> >generated. In this case that explanation matches with what we're
> >seeing here: two scope units for conmon and sleep and dynamically
> >generated.
> >
> >>Because of this, we recommend tracking Conmon, not Podman, with unit
> >>files. In Podman 1.5.0 and later, 'podman generate systemd' will
> >>properly handle this, creating a unit file that tracks Conmon using
> >>PID file.
> >
> >Can you illustrate an example of using systemd to track conmon instead
> >of podman?
>
> The unit file generated by `generate systemd` below is a good example
> of what we want to use - in contrast to using a `Type=simple` unit
> file using `podman start --attach` (which was previously recommended).
> As previously mentioned, Podman becomes effectively independent of the
> container when it's running - so the Podman process can disappear but
> the container may still be running, which is not conducive to the
> Type=simple unit.
>
> >
> >My goal is to have one way to stop, start, and enable my containers.
> >
> >In the example above I know I can check the status of the conmon scope
> >unit, it looks like the name comes from the container id:
> >
> >```
> ># systemctl status
>
>libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
> >● libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297
> > Loaded: loaded
> >Transient: yes
> > Drop-In: /run/systemd/system/libpod-conmon-a75a16081e23bb03589b214580b3226d8b2
> > └─50-DefaultDependencies.conf, 50-Delegate.conf, 50-Slice.conf
> > Active: active (running) since Mon 2019-08-12 17:20:17 UTC; 2min 20s ago
> > Tasks: 2
> > Memory: 200.0K
> > CPU: 17ms
> > CGroup: /machine.slice/libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a
> > └─22631 /usr/bin/conmon -s -c a75a16081e23bb03589b214580b3226d8b2ef77
> >
> >Aug 12 17:20:17 srv0 systemd[1]: Started libpod-conmon-a75a16081e23bb03589b21458
> ># podman ps
> >CONTAINER ID IMAGE COMMAND CREATED
> > STATUS PORTS NAMES
> >a75a16081e23 docker.io/library/alpine:latest sleep 9999 41 minutes
> >ago Up 22 minutes ago example
> ># systemctl show
>
>libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
> >| grep ExecStart
> >```
> >
> >I didn't see an ExecStart directive inside the scope unit.
> >
> >>podman generate systemd
> >
> >Ah, I see what you mean
> >
> >```
> ># podman generate systemd example > /etc/systemd/system/example.service
> ># systemctl daemon-reload
> ># systemctl cat example
> >[Unit]
> >Description=a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297 Pod
> >[Service]
> >Restart=on-failure
> >ExecStart=/usr/bin/podman start a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7
> >ExecStop=/usr/bin/podman stop -t 10 a75a16081e23bb03589b214580b3226d8b2ef77a382c
> >KillMode=none
> >Type=forking
> >PIDFile=/var/lib/containers/storage/overlay-containers/a75a16081e23bb03589b21458
> >[Install]
> >WantedBy=multi-user.target
> ># systemctl start example
> ># journalctl -u example | grep PID | tail -n 1
> >Aug 12 17:50:38 srv0 systemd[1]: example.service: PID file
>
>/var/lib/containers/storage/overlay-containers/a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297/userdata/a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.pid
> >not readable (yet?) after start: No such file or directory
> >```
> >
> >Is using `podman generate systemd example` planned for the future or
> >is it supposed to work now?
>
> It's bugged in 1.4.x - fixed in 1.5.0 (just released Friday).
>
> >
> >[1] https://github.com/containers/libpod/pull/3581
> >[2]
https://unix.stackexchange.com/questions/534843/why-is-conmon-in-a-differ...
> >[3] https://youtu.be/7CWmuhkgZWs?t=2204
> >
> >On Mon, Aug 12, 2019 at 7:01 AM Matt Heon <mheon(a)redhat.com> wrote:
> >>
> >> On 2019-08-10 13:17, Max Bigras wrote:
> >> >Given an alpine:3.10.1 image
> >> >
> >> >```
> >> >podman pull alpine:3.10.1
> >> >```
> >> >
> >> >And a unit file foo.service
> >> >
> >> >```
> >> >[Service]
> >> >ExecStart=/usr/bin/podman run --name %N --rm --tty alpine:3.10.1 sleep
99999
> >> >ExecStop=/usr/bin/podman stop %N
> >> >```
> >> >
> >> >And starting `foo.service` with `systemctl`
> >> >
> >> >```
> >> ># systemctl daemon-reload
> >> ># systemctl start foo.service
> >> >```
> >> >
> >> >I don't see my `sleep` process in `foo.service` status:
> >> >
> >> >```
> >> ># systemctl status foo.service | head
> >> >● foo.service
> >> > Loaded: loaded (/etc/systemd/system/foo.service; static; vendor
> >> >preset: enabled)
> >> > Active: active (running) since Sat 2019-08-10 19:58:05 UTC; 40s ago
> >> > Main PID: 15524 (podman)
> >> > Tasks: 9
> >> > Memory: 7.3M
> >> > CPU: 79ms
> >> > CGroup: /system.slice/foo.service
> >> > └─15524 /usr/bin/podman run --name foo --rm --tty
> >> >alpine:3.10.1 sleep 99999
> >> >```
> >> >
> >> >I see `conmon` land in a different cgroup, visible with the
> >> >`systemd-cgls` command:
> >> >
> >> >```
> >> ># systemd-cgls
> >> >Control group /:
> >> >-.slice
> >> >├─init.scope
> >> >│ └─1 /sbin/init
> >> >├─machine.slice
> >> >│
├─libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a
> >> >│ │ └─15648 /usr/bin/conmon -s -c
> >> >c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0
> >> >│
└─libpod-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
> >> >│ └─15662 sleep 99999
> >> >├─system.slice
> >> >│ ├─mdadm.service
> >> >│ │ └─880 /sbin/mdadm --monitor --pid-file /run/mdadm/monitor.pid
> >> >--daemonise --s
> >> >│ ├─foo.service
> >> >│ │ └─15524 /usr/bin/podman run --name foo --rm --tty alpine:3.10.1
sleep 99999
> >> >```
> >> >
> >> >From listening to youtube presentations about podman I thought podman
> >> >using a traditional fork exec model would imply all my processes would
> >> >show up in the same `systemctl status` and be in the same control
> >> >group controlled by systemd.
> >> >
> >> >Looking at the output of `ps` also shows that the `sleep` process is
> >> >the parent of the `conmon` process and not the `podman` process:
> >> >
> >> >```
> >> ># ps -Heo pid,ppid,comm,cgroup
> >> >15524 1 podman
> >> >11:memory:/system.slice/foo.service,8:pids:/system.sl
> >> >15648 1 conmon
> >> >11:memory:/machine.slice/libpod-conmon-c598f5a0c84881
> >> >15662 15648 sleep
> >> >11:memory:/machine.slice/libpod-c598f5a0c84881c69dcd6
> >> >```
> >> >
> >> >Instead it looks like `conmon` in a `scope` unit named:
> >> >
> >> >```
> >>
>libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
> >> >```
> >> >
> >> >Why doesn't `conmon` and `sleep` land in the same `foo.service`
systemd unit?
> >> >_______________________________________________
> >> >Podman mailing list -- podman(a)lists.podman.io
> >> >To unsubscribe send an email to podman-leave(a)lists.podman.io
> >>
> >> All Linux containers, at present, will create and manage their own
> >> CGroups, independent of systemd (with a few potential exceptions).
> >> This is mostly done so they can independently manage resources, though
> >> it is also necessary to do some common container operations - the
> >> 'podman stats' and 'podman top' commands, for example, track
processes
> >> in the container by its CGroup.
> >>
> >> The exception I mentioned was rootless containers in a CGroup v1
> >> environment. There is no support for delegation to rootless containers
> >> in the V1 hierarchy, so the containers have no permission to create
> >> CGroups.
> >>
> >> For most people, this is perfectly sufficient, but we definitely
> >> recognize that there are use cases that require keeping containers in
> >> CGroups managed elsewhere - most notably, from systemd unit files.
> >> There is work ongoing at [1] to enable this, though I caution that
> >> there are a lot of moving parts here - we don't just need support in
> >> Podman, but also in 'runc' - Podman isn't actually creating the
new
> >> CGroup for the container, the OCI runtime (usually 'runc') is.
> >>
> >> Also, a bit more context: the Conmon CGroup is not the container
> >> CGroup. Conmon creates its own CGroup (for various legacy reasons -
> >> we're evaluating whether these still hold true, and this could change)
> >> and then spawns the OCI runtime - and then the OCI runtime spawns its
> >> own CGroup. So you'll have a Conmon CGroup and another for the actual
> >> container (the two 'libpod' cgroups).
> >>
> >> The parent situation is simpler to explain; Podman launches conmon,
> >> and then conmon double-forks to daemonize. At that point, the two are
> >> effectively separate; Podman itself can go away completely, and the
> >> Conmon process will continue managing the container. This is
> >> deliberate - Podman is just the frontend that launches the container,
> >> and we don't need it to keep running once the container is started.
> >>
> >> Because of this, we recommend tracking Conmon, not Podman, with unit
> >> files. In Podman 1.5.0 and later, 'podman generate systemd' will
> >> properly handle this, creating a unit file that tracks Conmon using
> >> PID file.
> >>
> >> I hope this helps explain things.
> >>
> >> Thanks,
> >> Matt Heon
> >>
> >> [1] https://github.com/containers/libpod/pull/3581
10:12 a.m.
New subject: Why does conmon land in a different cgroup when using systemd and podman?
On 2019-08-12 12:06, Max Bigras wrote:
>It's bugged in 1.4.x - fixed in 1.5.0 (just released Friday).
Right on! I just installed a fresh podman package on Ubuntu 16.04 and
got version 1.5.0.
I made an example using the `--conmon-pidfile` flag to podman create.
I never made a custom pid file before so I'm searched around, it looks
like people write pid files to /var/run/foo.pid.
```
# podman create \
--name bar \
--tty \
--conmon-pidfile /var/run/bar.pid \
We're actually providing a default value for this now - if you don't
specify, it will be created somewhere in our internal temporary files
directory, so you can still use `generate systemd` on containers that
do not have it specified.
alpine \
/bin/sh -c 'while true; do date; sleep 1; done'
33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496
# podman generate systemd bar > /etc/systemd/system/bar.service
# systemctl daemon-reload
# systemctl start bar
# systemctl status bar
● bar.service - 33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496
Loaded: loaded (/etc/systemd/system/bar.service; disabled; vendor preset: ena
Active: active (running) since Mon 2019-08-12 18:53:22 UTC; 31s ago
Process: 15832 ExecStart=/usr/bin/podman start 33b7486fda2846ae780cef4913c3a46
Main PID: 15951 (conmon)
Tasks: 0
Memory: 364.0K
CPU: 71ms
CGroup: /system.slice/bar.service
‣ 15951 /usr/bin/conmon --api-version 1 -s -c 33b7486fda2846ae780cef4
Aug 12 18:53:22 srv0 systemd[1]: Starting 33b7486fda2846ae780cef4913c3a46be6005e
Aug 12 18:53:22 srv0 podman[15832]: 2019-08-12 18:53:22.43628578 +0000 UTC m=+0.
Aug 12 18:53:22 srv0 podman[15832]: 2019-08-12 18:53:22.443460842 +0000 UTC m=+0
Aug 12 18:53:22 srv0 podman[15832]: 33b7486fda2846ae780cef4913c3a46be6005e6bb75c
Aug 12 18:53:22 srv0 systemd[1]: Started 33b7486fda2846ae780cef4913c3a46be6005e6
# podman ps | grep bar
33b7486fda28 docker.io/library/alpine:latest /bin/sh -c while ...
40 seconds ago Up 18 seconds ago bar
# systemd-cgls /system.slice/bar.service
Control group /system.slice/bar.service:
# systemd-cgls /machine.slice
Control group /machine.slice:
├─libpod-33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496.scope
│ ├─15966 /bin/sh -c while true; do date; sleep 1; done
│ └─16234 sleep 1
└─libpod-conmon-33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496
└─15951 /usr/bin/conmon --api-version 1 -s -c 33b7486fda2846ae780cef4913c3a46b
```
`systemctl status` reports the conmon process is in the
/system.slice/bar.service cgroup but I'm not seeing the
/system.slice/bar.service cgroup in the output of `systemd-cgls`. And
instead only seeing the two new cgroups for the scope units in
/machine.slice
```
root@srv0:~# systemd-cgls /system.slice/bar.service
Control group /system.slice/bar.service:
root@srv0:~# systemd-cgls /machine.slice
Control group /machine.slice:
├─libpod-33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496.scope
│ ├─15966 /bin/sh -c while true; do date; sleep 1; done
│ └─16979 sleep 1
└─libpod-conmon-33b7486fda2846ae780cef4913c3a46be6005e6bb75cf9be09ef7868543d8496
└─15951 /usr/bin/conmon --api-version 1 -s -c 33b7486fda2846ae780cef4913c3a46b
```
Is `systemctl status` showing a CGroup that doesn't exist unexpected?
Hmmm.
My initial impression here is that Conmon spawned in that CGroup, but
then subsequently moved to the `libpod-conmon-$CID` CGroup - so this
seems like an artifact of our specific implementation.
On Mon, Aug 12, 2019 at 11:20 AM Matt Heon <mheon(a)redhat.com>
wrote:
>
> On 2019-08-12 10:56, Max Bigras wrote:
> >Thank you for the explanation and link to WIP PR #3581 [1]!
> >After reading your explanation and answers to my question on Stack
> >Exchange [2] I'm learning more about what's going on.
> >
> >>Also, a bit more context: the Conmon CGroup is not the container
> >>CGroup. Conmon creates its own CGroup (for various legacy reasons -
> >>we're evaluating whether these still hold true, and this could change)
> >>and then spawns the OCI runtime - and then the OCI runtime spawns its
> >>own CGroup. So you'll have a Conmon CGroup and another for the actual
> >>container (the two 'libpod' cgroups).
> >
> >I made an example illustrating the three cgroups you mentioned:
> >
> >1. /system.slice/example.service for my systemd service
> >2. /machine.slice/libpod-conmon-a75a16081e23b...scope for conmon
> >3. /machine.slice/libpod-a75a16081e23bb03589....scope for processes
> >inside the container (sleep in this case)
> >
> >```
> ># podman create --name example --tty alpine sleep 9999
> ># cat <<'EOF' > /etc/systemd/system/example.service
> >[Service]
> >ExecStart=/usr/bin/podman start --attach %N
> >ExecStop=/usr/bin/podman stop %N
> >EOF
> ># systemctl daemon-reload
> ># systemd-cgls /machine.slice
> >Control group /machine.slice
> ># systemctl start example
> ># systemd-cgls /machine.slice
> >Control group /machine.slice:
> >├─libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297
> >│ └─22385 /usr/bin/conmon -s -c a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7
> >└─libpod-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
> > └─22399 sleep 9999
> ># systemd-cgls /system.slice/example.service
> >Control group /system.slice/example.service:
> >└─22308 /usr/bin/podman start --attach example
> >```
> >
> >From listening to a presentation from Lennart on YouTube systemd and
> >Control Groups [3], I learned that the scope unit is just like the
> >service unit because it manages processes; however, the scope unit is
> >different from the service unit because scope units can be dynamically
> >generated. In this case that explanation matches with what we're
> >seeing here: two scope units for conmon and sleep and dynamically
> >generated.
> >
> >>Because of this, we recommend tracking Conmon, not Podman, with unit
> >>files. In Podman 1.5.0 and later, 'podman generate systemd' will
> >>properly handle this, creating a unit file that tracks Conmon using
> >>PID file.
> >
> >Can you illustrate an example of using systemd to track conmon instead
> >of podman?
>
> The unit file generated by `generate systemd` below is a good example
> of what we want to use - in contrast to using a `Type=simple` unit
> file using `podman start --attach` (which was previously recommended).
> As previously mentioned, Podman becomes effectively independent of the
> container when it's running - so the Podman process can disappear but
> the container may still be running, which is not conducive to the
> Type=simple unit.
>
> >
> >My goal is to have one way to stop, start, and enable my containers.
> >
> >In the example above I know I can check the status of the conmon scope
> >unit, it looks like the name comes from the container id:
> >
> >```
> ># systemctl status
>
>libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
> >● libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297
> > Loaded: loaded
> >Transient: yes
> > Drop-In: /run/systemd/system/libpod-conmon-a75a16081e23bb03589b214580b3226d8b2
> > └─50-DefaultDependencies.conf, 50-Delegate.conf, 50-Slice.conf
> > Active: active (running) since Mon 2019-08-12 17:20:17 UTC; 2min 20s ago
> > Tasks: 2
> > Memory: 200.0K
> > CPU: 17ms
> > CGroup: /machine.slice/libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a
> > └─22631 /usr/bin/conmon -s -c a75a16081e23bb03589b214580b3226d8b2ef77
> >
> >Aug 12 17:20:17 srv0 systemd[1]: Started libpod-conmon-a75a16081e23bb03589b21458
> ># podman ps
> >CONTAINER ID IMAGE COMMAND CREATED
> > STATUS PORTS NAMES
> >a75a16081e23 docker.io/library/alpine:latest sleep 9999 41 minutes
> >ago Up 22 minutes ago example
> ># systemctl show
>
>libpod-conmon-a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.scope
> >| grep ExecStart
> >```
> >
> >I didn't see an ExecStart directive inside the scope unit.
> >
> >>podman generate systemd
> >
> >Ah, I see what you mean
> >
> >```
> ># podman generate systemd example > /etc/systemd/system/example.service
> ># systemctl daemon-reload
> ># systemctl cat example
> >[Unit]
> >Description=a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297 Pod
> >[Service]
> >Restart=on-failure
> >ExecStart=/usr/bin/podman start a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7
> >ExecStop=/usr/bin/podman stop -t 10 a75a16081e23bb03589b214580b3226d8b2ef77a382c
> >KillMode=none
> >Type=forking
> >PIDFile=/var/lib/containers/storage/overlay-containers/a75a16081e23bb03589b21458
> >[Install]
> >WantedBy=multi-user.target
> ># systemctl start example
> ># journalctl -u example | grep PID | tail -n 1
> >Aug 12 17:50:38 srv0 systemd[1]: example.service: PID file
>
>/var/lib/containers/storage/overlay-containers/a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297/userdata/a75a16081e23bb03589b214580b3226d8b2ef77a382c5cf7845466823742b297.pid
> >not readable (yet?) after start: No such file or directory
> >```
> >
> >Is using `podman generate systemd example` planned for the future or
> >is it supposed to work now?
>
> It's bugged in 1.4.x - fixed in 1.5.0 (just released Friday).
>
> >
> >[1] https://github.com/containers/libpod/pull/3581
> >[2]
https://unix.stackexchange.com/questions/534843/why-is-conmon-in-a-differ...
> >[3] https://youtu.be/7CWmuhkgZWs?t=2204
> >
> >On Mon, Aug 12, 2019 at 7:01 AM Matt Heon <mheon(a)redhat.com> wrote:
> >>
> >> On 2019-08-10 13:17, Max Bigras wrote:
> >> >Given an alpine:3.10.1 image
> >> >
> >> >```
> >> >podman pull alpine:3.10.1
> >> >```
> >> >
> >> >And a unit file foo.service
> >> >
> >> >```
> >> >[Service]
> >> >ExecStart=/usr/bin/podman run --name %N --rm --tty alpine:3.10.1 sleep
99999
> >> >ExecStop=/usr/bin/podman stop %N
> >> >```
> >> >
> >> >And starting `foo.service` with `systemctl`
> >> >
> >> >```
> >> ># systemctl daemon-reload
> >> ># systemctl start foo.service
> >> >```
> >> >
> >> >I don't see my `sleep` process in `foo.service` status:
> >> >
> >> >```
> >> ># systemctl status foo.service | head
> >> >● foo.service
> >> > Loaded: loaded (/etc/systemd/system/foo.service; static; vendor
> >> >preset: enabled)
> >> > Active: active (running) since Sat 2019-08-10 19:58:05 UTC; 40s ago
> >> > Main PID: 15524 (podman)
> >> > Tasks: 9
> >> > Memory: 7.3M
> >> > CPU: 79ms
> >> > CGroup: /system.slice/foo.service
> >> > └─15524 /usr/bin/podman run --name foo --rm --tty
> >> >alpine:3.10.1 sleep 99999
> >> >```
> >> >
> >> >I see `conmon` land in a different cgroup, visible with the
> >> >`systemd-cgls` command:
> >> >
> >> >```
> >> ># systemd-cgls
> >> >Control group /:
> >> >-.slice
> >> >├─init.scope
> >> >│ └─1 /sbin/init
> >> >├─machine.slice
> >> >│
├─libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a
> >> >│ │ └─15648 /usr/bin/conmon -s -c
> >> >c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0
> >> >│
└─libpod-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
> >> >│ └─15662 sleep 99999
> >> >├─system.slice
> >> >│ ├─mdadm.service
> >> >│ │ └─880 /sbin/mdadm --monitor --pid-file /run/mdadm/monitor.pid
> >> >--daemonise --s
> >> >│ ├─foo.service
> >> >│ │ └─15524 /usr/bin/podman run --name foo --rm --tty alpine:3.10.1
sleep 99999
> >> >```
> >> >
> >> >From listening to youtube presentations about podman I thought podman
> >> >using a traditional fork exec model would imply all my processes would
> >> >show up in the same `systemctl status` and be in the same control
> >> >group controlled by systemd.
> >> >
> >> >Looking at the output of `ps` also shows that the `sleep` process is
> >> >the parent of the `conmon` process and not the `podman` process:
> >> >
> >> >```
> >> ># ps -Heo pid,ppid,comm,cgroup
> >> >15524 1 podman
> >> >11:memory:/system.slice/foo.service,8:pids:/system.sl
> >> >15648 1 conmon
> >> >11:memory:/machine.slice/libpod-conmon-c598f5a0c84881
> >> >15662 15648 sleep
> >> >11:memory:/machine.slice/libpod-c598f5a0c84881c69dcd6
> >> >```
> >> >
> >> >Instead it looks like `conmon` in a `scope` unit named:
> >> >
> >> >```
> >>
>libpod-conmon-c598f5a0c84881c69dcd69c5af981dd5071385138e45ce0c3b94dcc5308953a5.scope
> >> >```
> >> >
> >> >Why doesn't `conmon` and `sleep` land in the same `foo.service`
systemd unit?
> >> >_______________________________________________
> >> >Podman mailing list -- podman(a)lists.podman.io
> >> >To unsubscribe send an email to podman-leave(a)lists.podman.io
> >>
> >> All Linux containers, at present, will create and manage their own
> >> CGroups, independent of systemd (with a few potential exceptions).
> >> This is mostly done so they can independently manage resources, though
> >> it is also necessary to do some common container operations - the
> >> 'podman stats' and 'podman top' commands, for example, track
processes
> >> in the container by its CGroup.
> >>
> >> The exception I mentioned was rootless containers in a CGroup v1
> >> environment. There is no support for delegation to rootless containers
> >> in the V1 hierarchy, so the containers have no permission to create
> >> CGroups.
> >>
> >> For most people, this is perfectly sufficient, but we definitely
> >> recognize that there are use cases that require keeping containers in
> >> CGroups managed elsewhere - most notably, from systemd unit files.
> >> There is work ongoing at [1] to enable this, though I caution that
> >> there are a lot of moving parts here - we don't just need support in
> >> Podman, but also in 'runc' - Podman isn't actually creating the
new
> >> CGroup for the container, the OCI runtime (usually 'runc') is.
> >>
> >> Also, a bit more context: the Conmon CGroup is not the container
> >> CGroup. Conmon creates its own CGroup (for various legacy reasons -
> >> we're evaluating whether these still hold true, and this could change)
> >> and then spawns the OCI runtime - and then the OCI runtime spawns its
> >> own CGroup. So you'll have a Conmon CGroup and another for the actual
> >> container (the two 'libpod' cgroups).
> >>
> >> The parent situation is simpler to explain; Podman launches conmon,
> >> and then conmon double-forks to daemonize. At that point, the two are
> >> effectively separate; Podman itself can go away completely, and the
> >> Conmon process will continue managing the container. This is
> >> deliberate - Podman is just the frontend that launches the container,
> >> and we don't need it to keep running once the container is started.
> >>
> >> Because of this, we recommend tracking Conmon, not Podman, with unit
> >> files. In Podman 1.5.0 and later, 'podman generate systemd' will
> >> properly handle this, creating a unit file that tracks Conmon using
> >> PID file.
> >>
> >> I hope this helps explain things.
> >>
> >> Thanks,
> >> Matt Heon
> >>
> >> [1] https://github.com/containers/libpod/pull/3581
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5 comments
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participants (2)
-
Matt Heon -
Max Bigras