processtitle 1.0

Customize process "title" as reported by ps and similar tools

processtitle

This Python extension module allows you to customize process "title" as reported by ps, top, Activity Monitor, Task Manager and similar tools.

It is similar to the well known py-setproctitle module but, not being constrained by backward compatibility, does things a bit differently and, hopefully, makes things more convenient for a user. (If you are already familiar with py-setproctitle make sure to read differences from py-setproctitle section.)

Modifying process title is useful in many cases. When you have many Python scripts, or, worse, many instances of the same Python script running on your system it is very hard to understand which one is which, if all you see in your process list is "Python" or "python3 same-script". Using this module allows your script to specify what it is for or what it is doing to be shown in the process list instead.

• Platform support
• Requirements
• Installing
• Usage
• Thread and other safety
• Differences from py-setproctitle
• Platform details
  • Linux
  • macOS
  • Windows
  • BSDs
  • Illumos

Platform support

The module will happily run and do nothing on any compatible system but the ones where it actually works (i.e. changes the process title) are: Linux, macOS, Windows, {Free|Net|Open}BSD and Illumos. See platform details below for more information about each platform.

In all cases only reasonably recent versions of each platform are supported. No attempt is made to work on ancient Linux kernels, Windows XP etc. etc. If you are stuck with a very old system your best bet is py-setproctitle.

Requirements

• Python >= 3.10 capable of loading native extensions. In particular, CPython, PyPy and GraalPy are all supported.
• If your platform doesn't have a binary wheel available, you will need:
  • A C++ compiler capable of compiling C++20 (GCC 10.2 or above and CLang 13 or above are known to work)
  • Python development libraries available (like python3-dev package in most Linux distributions)

Installing

pip install processtitle

Usage

import processtitle

processtitle.prepare(...optional config params...)

if not processtitle.set_to("my fancy process"):
    print("ooops, process title couldn't be set")
else:
    print(f"last set process title is {processtitle.last_set()}")

The processtitle.prepare currently has the following keyword-only optional parameters defined:

fork_safe_only: bool = False : use only such external libraries and/or APIs that are safe if your process later performs a fork without exec. Currently this is only relevant on macOS where APIs needed to update title in Activity Monitor are not fork-safe and will cause crashes if used together with fork without exec.

If you wish to enable debug output from this module you can use standard logging machinery:

import logging

logging.basicConfig(...)
logging.getLogger("processtitle").setLevel(logging.DEBUG)

Alternatively, you can use py-setproctitle compatible method by setting SPT_DEBUG environment variable to a non-empty value (which is not "0"). For example:

SPT_DEBUG=1 your_script_that_uses_processtitle

Thread and other safety

processtitle itself is thread-safe - all its operations are protected by a mutex. However, the effects of changing process title are not. On every platform, changing the title modifies some globals process information. If this information is accessed by another thread at the same time Bad Things Will Happen. Therefore, it is advisable to only change the title before other threads are running or when you are absolutely sure they are suspended.

On some platforms, processtitle modifies pointers visible to native code (for example argv[1]... and environ on many Unix systems). It never deallocates the memory pointed by these so any native code that uses cached values of such pointer should be safe. Python's sys.argv and os.environ should be completely unaffected by any of these manipulations.

Differences from py-setproctitle

The most notable difference between processtitle and py-setproctitle is that this library requires you to call processtitle.prepare() before setting the process title. Absolutely nothing is done prior to prepare - just importing the module has no side effects. The prepare() method arguments allow you to customize library behavior on platforms where multiple incompatible behaviors are possible. Currently this affects only macOS (see macOS details below) but in the future might be extended to other platforms.

In addition:

• There is no requirement to import processtitle as early as possible. It does not rely on Python interpreter state which may be changed by other libraries
• There is no general "get process title" call (instead you can query the last title you set via last_set()). This is because querying the original title might not be possible on some platforms.
• Currently there are no "set/get thread title" calls. If there is any interest, they may be added in the future.
• processtitle supports Windows. At the time of this writing py-setproctitle does not.
• Wherever possible processtitle avoids tinkering with argv and relies on other safer, documented or semi-documented methods.
• processtitle uses standard Python logging module to produce diagnostic output rather than just printing to stdout. (For compatibility, SPT_DEBUG environment variable is also supported - it simply sets the default logging level for this module to logging.DEBUG)
• processtitle is written in C++, not C, so it requires a reasonably modern C++ compiler when binary wheels are not available.
• processtitle does not support old or no longer maintained operating systems like AIX, HP-UX etc.

Platform details

Linux

On Linux you will be able to see the process title in the output of ps or top commands, as well, as with any other tool that displays process info.

To change the title, processtitle uses the following methods:

• PR_SET_MM call.
• PR_SET_NAME call.

processtitle.set_to() returns True if at least one of these methods succeeded.

macOS

On macOS there are 2 independent places where process title is shown: ps, top and similar commands and Activity Monitor. They take information from completely different places and modifying one doesn't modify the other. Unfortunately, the API required to change the title for Activity Monitor cannot be used if your process later fork()-s without exec(). If used in such a process, the forked process will most likely crash randomly and unpredictably. Note that some popular libraries such as gunicorn may use fork() internally.

[!IMPORTANT] Using fork without exec in Python on macOS (or any other platform) is, in general, dangerous because you rarely know for sure whether the libraries your code depends upon are fork-safe. This is why multiprocessing library avoids fork by default on macOS and, recently, on all platforms.

Because of this issue, if you must use fork() on macOS you have two options:

1. Pass fork_safe_only=True argument to processtitle.prepare() in the parent process. Doing so will prevent use of any non-fork-safe APIs but will also preclude customized process title from being shown in Activity Monitor.

2. Alternatively, if feasible, call processtitle.prepare() after the last fork() in the parent process.

To change the title, processtitle uses the following methods:

• Changing the content of native (not Python's) argv[0] (while preserving the rest of argv and relocating environ).
• If fork_safe_only is False undocumented Launch Services calls

processtitle.set_to() returns True if at least one of these methods succeeded.

Windows

On Windows you can see the process by looking at the process command line. You can see the command lines of running processes in two ways:

1. Using powershell's Get-WmiObject Win32_Process call:

Get-WmiObject Win32_Process | Select-Object ProcessId, CommandLine

If you use cmd as your command interpreter you can achieve the same effect via:

powershell -c "Get-WmiObject Win32_Process | Select-Object ProcessId, CommandLine"

2. In Task Manager details view. If the "Command Line" column is not present, right-click the columns header, choose "Select columns" and check "Command Line" entry in the list.

To change the title, processtitle uses modifies/replaces partially-documented RTL_USER_PROCESS_PARAMETERS via undocumented or partially documented calls.

BSDs

On {Free|Net|Open}BSD you will be able to see the process title in the output of ps or top commands, as well, as with any other tool that displays process info. All of these platforms will, in general, add the original executable name (e.g. python3) to the actual title either as a prefix or a suffix.

To change the title, processtitle uses documented setproctitle() call (FreeBSD, NetBSD, OpenBSD).

Illumos

On Illumos by default the ps command shows process title captured at process creation. To see the current one pass the -F option.

To change the title, processtitle changes the content of native (not Python's) argv[0] (while preserving the rest of argv and relocating environ).