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On Ubuntu 16.04/ppc64el, the cgroup for a user session (bash) inherits
from a sshd.service, when the user logs into the machine using SSH.
This causes the amount of process to be limited by
/etc/systemd/system/conf DefaultTasksMax=512
This does not seem to happen on amd64. This is a cgroup tree diff:
On x64, bash (in this case, PID 19405 ) spawned by sshd belongs to CGROUP
session-5.scope->user-1003.slice->user.slice:
└─user.slice
├─user-1000.slice
│ ├─session-1.scope
│ │ ├─634 sshd: brenohl [priv]
│ │ ├─660 sshd: brenohl@pts/0
│ │ └─661 -bash
│ └─user@1000.service
│ ├─636 /lib/systemd/systemd --user
│ └─637 (sd-pam)
└─user-1003.slice
├─session-5.scope
│ ├─19379 sshd: gromero [priv]
│ ├─19404 sshd: gromero@pts/1
│ ├─19405 -bash
However, in ppc64le, bash (in this case, PID 1913), spawned by sshd
belongs to CGROUP ssh.service->system.slice->-.slice:
-.slice
├─1720 /sbin/cgmanager -m name=systemd
├─init.scope
└─system.slice
├─dbus.service
│ └─1699 /usr/bin/dbus-daemon --system --address=systemd: --nofork
--nopidfile --systemd-activation
├─cron.service
│ └─1702 /usr/sbin/cron -f
├─ifup@eth0.service
│ └─1833 /sbin/dhclient
├─accounts-daemon.service
│ └─1717 /usr/lib/accountsservice/accounts-daemon
├─system-serial\x2dgetty.slice
│ └─serial-getty@hvc0.service
│ └─1875 /sbin/agetty --keep-baud 115200 38400 9600 hvc0 vt220
├─systemd-journald.service
│ └─1382 /lib/systemd/systemd-journald
├─systemd-timesyncd.service
│ └─1639 /lib/systemd/systemd-timesyncd
├─ssh.service
│ ├─1863 /usr/sbin/sshd -D
│ ├─1897 sshd: gromero [priv]
│ ├─1912 sshd: gromero@pts/0
│ ├─1913 -bash
Having the user session associated with the systemd cgroups
(/system.slice/ssh.service) instead of normal user/session cgroups (as
user-XXXX.slice/session-5.scope), causes the process to be limited to the
systemd TasksMax limit, thus, causing "Cannot fork" and "Resource temporary
unavailable" problems when the amount of processes reaches this 512 limit.
Gustavo Romero has more details about this problem, and will comment
soon.
** Affects: ubuntu-meta (Ubuntu)
Importance: Critical
Assignee: Martin Pitt (pitti)
Status: In Progress
** Tags: ppc64el
--
ppc64el ubuntu-server ISO does not install libpam-systemd (not installing
recommends?)
https://bugs.launchpad.net/bugs/1561658
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