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Os Syscall Prctl

DodaTech 1 min read

In this tutorial, you'll learn about How to Fix prctl Errors. We cover key concepts, practical examples, and best practices.

Fix prctl errors when PR_SET_NAME not set causing all threads identified by process name.

Quick Fix

Wrong

import os, threading, ctypes
libc=ctypes.CDLL('libc.so.6')
def worker():
    libc.prctl(15, b'worker-thread')  # PR_SET_NAME=15
    while True: pass
for i in range(4):
    threading.Thread(target=worker, daemon=True).start()
# ps -T -p PID shows all threads named 'python'

Threads not named. Debugging: all threads show same process name. Can't identify which thread is which.

import os, threading, ctypes
libc=ctypes.CDLL('libc.so.6')
PR_SET_NAME=15  # per-thread name
PR_SET_NAME_MM=35  # per-process name
class NamedThread(threading.Thread):
    def __init__(self, name, target):
        super().__init__(target=target)
        self.thread_name=name
    def run(self):
        libc.prctl(PR_SET_NAME, self.thread_name.encode())
        super().run()
def worker(): pass
t=NamedThread('worker-1', worker); t.start()
t.join()
# Check: ps -T -p PID shows 'worker-1'

Thread named 'worker-1'. 'ps -T' shows per-thread names. Debugging easier.

Prevention

Use prctl(PR_SET_NAME, ...) per thread. 'ps -T -p [PID]' shows thread names.

DodaTech Tools

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FAQ

What is prctl?

Process control operations. Set thread name, capabilities, seccomp, personality.

PR_SET_NAME?

Set thread/process name visible in ps. 15 characters max. Per-thread.

Other prctl uses?

PR_SET_SECCOMP (sandbox), PR_SET_NO_NEW_PRIVS, PR_CAP_AMBIENT, PR_GET_PDEATHSIG.

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