proc_tid_children - Man Page

/proc/tid/children (since Linux 3.5)

A space-separated list of child tasks of this task. Each child task is represented by its TID.

This option is intended for use by the checkpoint-restore (CRIU) system, and reliably provides a list of children only if all of the child processes are stopped or frozen. It does not work properly if children of the target task exit while the file is being read! Exiting children may cause non-exiting children to be omitted from the list. This makes this interface even more unreliable than classic PID-based approaches if the inspected task and its children aren't frozen, and most code should probably not use this interface.

Until Linux 4.2, the presence of this file was governed by the CONFIG_CHECKPOINT_RESTORE kernel configuration option. Since Linux 4.2, it is governed by the CONFIG_PROC_CHILDREN option.

proc(5)