operation can be used to discover the parental relationship
between user namespaces; see
.BR ioctl_ns (2).
+.PP
+A task that changes one of its effective IDs
+will have its dumpability reset to the value in
+.IR /proc/sys/fs/suid_dumpable .
+This may affect the ownership of proc files of child processes
+and may thus cause the parent to lack the permissions
+to write to mapping files of child processes running in a new user namespace.
+In such cases making the parent process dumpable, using
+.B PR_SET_DUMPABLE
+in a call to
+.BR prctl (2),
+before creating a child process in a new user namespace may rectify this problem.
+See
+.BR prctl (2)
+and
+.BR proc (5)
+for details on how ownership is affected.
.\"
.\" ============================================================
.\"