Os Syscall Uid Gid
DodaTech
1 min read
In this tutorial, you'll learn about How to Fix User/Group ID Errors. We cover key concepts, practical examples, and best practices.
Fix user/group id errors when process running with wrong UID/GID causes permission errors.
Quick Fix
Wrong
import os
os.setuid(1000) # PermissionError if not root!
Only root can set arbitrary UID. CAP_SETUID required.
Right
import os, pwd
# Check current UID/GID:
print(f'UID: {os.getuid()}, EUID: {os.geteuid()}')
print(f'GID: {os.getgid()}, EGID: {os.getegid()}')
# Set real UID (requires root):
if os.geteuid()==0:
os.setuid(1000) # sets real, effective, saved UIDs
print(f'Now running as UID {os.getuid()}')
# Or use saved-set-user-ID:
# When started as root: seteuid(1000) # set effective only, can revert
# Drop privileges permanently:
def drop_privileges():
if os.geteuid()!=0: return
# Set GID first, then UID:
os.setgid(1000)
os.setuid(1000)
print(f'Dropped to UID {os.getuid()}')
# Check supplementary groups:
print(f'Groups: {os.getgroups()}')
# Add group:
try: os.setgroups([1000, 1001])
except: print('Need root for setgroups')
Process UID/GID properly set. Permission correct for target user.
Prevention
setuid requires root or CAP_SETUID. Check getuid/geteuid before setuid operations.
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