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cgroups.7: Add some details to discussion of cgroup.procs file 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2016-10-07 14:04:43 +02:00
parent 31ec2a5cf7
commit f524e7f8c7
1 changed files with 22 additions and 5 deletions
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27
man7/cgroups.7
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@ -236,20 +236,37 @@ A new cgroup is created by creating a directory in the cgroup filesystem:
mkdir /sys/fs/cgroup/cpu/cg1
This creates a new empty cgroup.
Processes may be moved to this cgroup by writing
their PIDs into the cgroup's
A process may be moved to this cgroup by writing its PID into the cgroup's
.I cgroup.procs
file:
echo $$ > /sys/fs/cgroup/cpu/cg1/cgroup.procs
The same file can be read to obtain a list of the processes
that are currently in
.IR cg1 .
Only one PID at a time should be written to this file.
Writing the value 0 to a
.IR cgroup.procs
file causes the writing process to be moved to the corresponding cgroup.
When writing a PID into the
.IR cgroup.procs ,
all threads in the process are moved into the new cgroup at once.
Within a hierarchy, a process can be a member of exactly one cgroup.
Writing a process's PID to a
.IR cgroup.procs
file automatically removes it from the cgroup of
which it was previously a member.
The
.I cgroup.procs
file can be read to obtain a list of the processes that are
members of a cgroup.
The returned list of PIDs is not guaranteed to be in order.
Nor is it guaranteed to be free of duplicates.
(For example, a PID may be recycled while reading from the list.)
In cgroups v1 (but not cgroups v2), an individual thread can be moved to
another cgroup by writing its thread ID
(i.e., the kernel thread ID returned by