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