Martin Panter <vadmium...@gmail.com> added the comment: Presumuing your file descriptor 3 is the read end of the pipe to the child’s output, then there is probably a process somewhere that could still write to the write end. Normally “check_output” waits until it has read all possible output from the pipe(s).
This is probably not a bug in Python. Maybe it is a bug with SSH or your “MUX” (you didn’t explain what that is) leaving a process running in the background that could output to stderr. Try to track down what processes have your pipe open. Find out the number that identifies the pipe. It is the node number in the “lsof” command, or in the symbolic link under /proc: $ lsof -a -c python -d 3 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME python3 26025 vadmium 3r FIFO 0,8 0t0 4913217 pipe $ ls -l "/proc/$(pgrep python)/fd/3" lr-x------ 1 vadmium vadmium 64 Oct 6 22:17 /proc/26025/fd/3 -> pipe:[4913217] Then look through the other files to find if other process(es) have the write end of the pipe open; “cat” in my example: $ lsof | grep 4913217 python3 26025 vadmium 3r FIFO 0,8 0t0 4913217 pipe cat 26026 vadmium 1w FIFO 0,8 0t0 4913217 pipe $ ls -l /proc/*/fd/* | grep 4913217 lr-x------ 1 vadmium vadmium 64 Oct 6 22:17 /proc/26025/fd/3 -> pipe:[4913217] l-wx------ 1 vadmium vadmium 64 Oct 6 22:16 /proc/26026/fd/1 -> pipe:[4913217] The general problem does seem to be a recurring thing with the subprocess module, so maybe more documentation or other enhancements could help. Similar reports: * Issue 31447: communicate not respecting timeout due to grandchild process * Issue 30154: subprocess.run with timeout and output pipe from grandchild * Issue 26534: check_output with shell=True and timeout doesn’t kill shell’s child * Issue 23213: communicate hang with stderr leaked in “systemd” daemon * Issue 13422: communicate hangs as long as a daemon leaves pipes open * Issue 4216: communicate hang after starting “cpboot” service ---------- nosy: +martin.panter _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue31712> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
