1 =========================
2 Process Number Controller
3 =========================
4
5 Abstract
6 --------
7
8 The process number controller is used to allow
9 new tasks from being fork()'d or clone()'d aft
10
11 Since it is trivial to hit the task limit with
12 place, PIDs are a fundamental resource. As suc
13 preventable in the scope of a cgroup hierarchy
14 the number of tasks in a cgroup.
15
16 Usage
17 -----
18
19 In order to use the `pids` controller, set the
20 pids.max (this is not available in the root cg
21 number of processes currently in the cgroup is
22
23 Organisational operations are not blocked by c
24 to have pids.current > pids.max. This can be d
25 be smaller than pids.current, or attaching eno
26 that pids.current > pids.max. However, it is n
27 policy through fork() or clone(). fork() and c
28 creation of a new process would cause a cgroup
29
30 To set a cgroup to have no limit, set pids.max
31 all new cgroups (N.B. that PID limits are hier
32 limit in the hierarchy is followed).
33
34 pids.current tracks all child cgroup hierarchi
35 superset of parent/child/pids.current.
36
37 The pids.events file contains event counters:
38
39 - max: Number of times fork failed in the cg
40 self or ancestors.
41
42 Example
43 -------
44
45 First, we mount the pids controller::
46
47 # mkdir -p /sys/fs/cgroup/pids
48 # mount -t cgroup -o pids none /sys/fs
49
50 Then we create a hierarchy, set limits and att
51
52 # mkdir -p /sys/fs/cgroup/pids/parent/
53 # echo 2 > /sys/fs/cgroup/pids/parent/
54 # echo $$ > /sys/fs/cgroup/pids/parent
55 # cat /sys/fs/cgroup/pids/parent/pids.
56 2
57 #
58
59 It should be noted that attempts to overcome t
60 fail::
61
62 # cat /sys/fs/cgroup/pids/parent/pids.
63 2
64 # ( /bin/echo "Here's some processes f
65 sh: fork: Resource temporary unavailab
66 #
67
68 Even if we migrate to a child cgroup (which do
69 not be able to overcome the most stringent lim
70 parent's)::
71
72 # echo $$ > /sys/fs/cgroup/pids/parent
73 # cat /sys/fs/cgroup/pids/parent/pids.
74 2
75 # cat /sys/fs/cgroup/pids/parent/child
76 2
77 # cat /sys/fs/cgroup/pids/parent/child
78 max
79 # ( /bin/echo "Here's some processes f
80 sh: fork: Resource temporary unavailab
81 #
82
83 We can set a limit that is smaller than pids.c
84 processes from being forked at all (note that
85 pids.current)::
86
87 # echo 1 > /sys/fs/cgroup/pids/parent/
88 # /bin/echo "We can't even spawn a sin
89 sh: fork: Resource temporary unavailab
90 # echo 0 > /sys/fs/cgroup/pids/parent/
91 # /bin/echo "We can't even spawn a sin
92 sh: fork: Resource temporary unavailab
93 #
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