ProcessLookupError with rare combination of start/stop/pause buttons on a slow system

[buhtz]

Introduction

Welcome to the project, if you pick up this Issue because of the
"GOOD FIRST USE" label. You will be mentored through the process if you
want. First the Issue is explained. At the end you will find some
guidance for first contributors. Please do not hesitate to ask questions.
Your solution don't need to be perfect.

Participation or contribution is not recommended unless you are familiar with Back In Time and are an active user. This project is not intended for learning basic Python skills or enhancing your GitHub profile.

Description of the problem

While manual testing the qt6 migration and clicking wild around in the GUI I discovered an Issue.

It seems to happen only in a rare (unusual) combination of the buttons to start, pause and stop a snapshot. My hypothesis is that I can trigger the problem because I am (as the user) are to fast and my system (a RaspberryPi4) is to slow. I assume this is not critical and not urgent.

That is the relevant error message.

DEBUG: [common/pluginmanager.py:249 PluginManager.load] Probing plugin systrayiconplugin.py
Traceback (most recent call last):
  File "/usr/share/backintime/qt/app.py", line 469, in <lambda>
    lambda: os.kill(self.snapshots.pid(), signal.SIGSTOP), None,
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ProcessLookupError: [Errno 3] Kein passender Prozess gefunden
Aborted

Steps to reproduce

Reproduce it with the following steps:

1. Press take snapshot button.
2. Press the stop button some seconds later. On my Pi4 2-3 seconds. You will observe in the terminal window behind that there are still some log lines produced.
3. Press take snapshot button again.
4. Press pause button quit quickly. The GUI crash with a ProcessLookupError but in the terminal window you do see that there is still activity in the background.

This screencast illustrate how to reproduce it.

Diagnostic output

{
    "backintime": {
        "name": "Back In Time",
        "version": "1.4.2-dev",
        "latest-config-version": 6,
        "local-config-file": "/home/UsernameReplaced/.config/backintime/config",
        "local-config-file-found": true,
        "global-config-file": "/etc/backintime/config",
        "global-config-file-found": false,
        "started-from": "/usr/share/backintime/common",
        "running-as-root": false,
        "user-callback": "/home/UsernameReplaced/.config/backintime/user-callback",
        "keyring-supported": true
    },
    "host-setup": {
        "platform": "Linux-6.1.0-13-arm64-aarch64-with-glibc2.36",
        "system": "Linux #1 SMP Debian 6.1.55-1 (2023-09-29)",
        "OS": {
            "/etc/os-release": "Debian GNU/Linux 12 (bookworm)",
            "/etc/debian_version": "12.4\n"
        },
        "display-system": "x11",
        "locale": "de_DE, UTF-8",
        "PATH": "/home/UsernameReplaced/.local/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games:/home/UsernameReplaced/.local/bin:/home/UsernameReplaced/.local/bin",
        "RSYNC_OLD_ARGS": "(not set)",
        "RSYNC_PROTECT_ARGS": "(not set)"
    },
    "python-setup": {
        "python": "3.11.2 main Mar 13 2023 12:18:29 CPython GCC 12.2.0",
        "python-executable": "/usr/bin/python3",
        "python-executable-symlink": true,
        "python-executable-resolved": "/usr/bin/python3.11",
        "sys.path": [
            "/usr/share/backintime/qt/plugins",
            "/usr/share/backintime/common/plugins",
            "/usr/share/backintime/plugins",
            "/usr/share/backintime/common",
            "/usr/share/backintime/qt",
            "/usr/lib/python311.zip",
            "/usr/lib/python3.11",
            "/usr/lib/python3.11/lib-dynload",
            "/usr/local/lib/python3.11/dist-packages",
            "/usr/lib/python3/dist-packages",
            "/usr/lib/python3.11/dist-packages"
        ],
        "qt": {
            "Version": "PyQt 6.4.2 / Qt 6.4.2",
            "Theme": "Tango",
            "Theme Search Paths": [
                "/usr/local/share/icons",
                "/usr/share/icons",
                ":/icons"
            ],
            "Fallback Theme": "",
            "Fallback Search Paths": []
        }
    },
    "external-programs": {
        "rsync": {
            "version": "3.2.7",
            "protocol": "31.0",
            "capabilities": {
                "file_bits": 64,
                "inum_bits": 64,
                "timestamp_bits": 64,
                "long_int_bits": 64,
                "socketpairs": true,
                "symlinks": true,
                "symtimes": true,
                "hardlinks": true,
                "hardlink_specials": true,
                "hardlink_symlinks": true,
                "IPv6": true,
                "atimes": true,
                "batchfiles": true,
                "inplace": true,
                "append": true,
                "ACLs": true,
                "xattrs": true,
                "secluded_args": "optional",
                "iconv": true,
                "prealloc": true,
                "stop_at": true,
                "crtimes": false
            },
            "optimizations": {
                "SIMD_roll": false,
                "asm_roll": false,
                "openssl_crypto": true,
                "asm_MD5": false
            },
            "checksum_list": [
                "xxh128",
                "xxh3",
                "xxh64",
                "md5",
                "md4",
                "sha1",
                "none"
            ],
            "compress_list": [
                "zstd",
                "lz4",
                "zlibx",
                "zlib",
                "none"
            ],
            "daemon_auth_list": [
                "sha512",
                "sha256",
                "sha1",
                "md5",
                "md4"
            ]
        },
        "ssh": "OpenSSH_9.2p1 Debian-2+deb12u1, OpenSSL 3.0.11 19 Sep 2023",
        "sshfs": "3.7.3",
        "encfs": "(no encfs)",
        "shell": "/bin/bash",
        "shell-version": "GNU bash, version 5.2.15(1)-release (aarch64-unknown-linux-gnu)"
    }
}

Your next steps

1. If this is your first contribution in this project please introduce
   your self and tell us about your skills, wishes and plans. Also let us
   know how you found the issue and the project.
2. Read the existing contributors documentation.
3. We can develop the next steps in the further discussion. Don't hesitate to ask.

What need to be done?

Try to reproduce the problem and investigate it. Describe the reason why this happens. After discussing a solution this could also be implemented by a contributor.

[GauranshMathur]

Hi, I would like to be assigned to this issue.

I am a fresh grad and I'm looking at opportunities that can help me better learn coding in linux systems and also be able to work on my python skills. I found this issue via good first issues tag on github.

I also saw that I can be mentored for this project which would be helpful.

I have read the contributions.md but am currently having a problem running the created qt4 deb file to be able to test the system, I have been able to complete the steps before that

[aryoda]

Hi, I would like to be assigned to this issue.

Welcome @GauranshMathur - we can need your help and there is still so much work to do :-)

I have read the contributions.md but am currently having a problem running the created qt4 deb file

Could you please describe in which of the steps described in CONTRIBUTING.md you are creating a qt4 deb file since seems outdated by far (we are using Qt6 now and do no longer support building a deb file anymore - this is done by distro maintainers only now).

Normally you just have to create run config in your prefered IDE (in my case: PyCharm Community Edition) and execute the file backintime/qt/app.py to start the GUI via the IDE - there is no need to install the dev version during development, an installed older version of BiT is enough (to have a running D-Bus service required for some operations - mainly cron-related)...

[GauranshMathur]

Hi @aryoda the part in the readme where to be able to contribute it asks to build a Deb file before testing is where this issue stems. So I was following those steps to be able to recreate the issue.

As you say you are on qt6, I may believe these instructions are old so I may need some assistance with the current method of building and testing.

[aryoda]

Hi @aryoda the part in the readme where to be able to contribute it asks to build a Deb file before testing is where this issue stems. So I was following those steps to be able to recreate the issue.

THX, now I have discovered this part too and yes, it is outdated - we need to remove it (it even was not generic enough since other distros may require other installation packages than deb).

As you say you are on qt6, I may believe these instructions are old so I may need some assistance with the current method of building and testing.

Basically you need to

• install BiT from your distro to get most of the dependencies installed on your system
• install all missing further dependencies (as described in the contributing.md)
• build via make as described in this section - but do not execute the sudo make install commands since you already have an installed version
• if the unit tests (make test) did succeed without errors (skips are allowed due to missing infrastructure like ssh) you can use your Python IDE of choice to start debugging by executing backintime/qt/app.py (add --debug as argument if you want to see more logging details in the console while running BiT in the IDE.)

If some unit tests fail it is most probably due to missing dependencies (Python packages etc.) and I will help you if this happens (I need your distro name + version and the error message of the unit test for this)...

[aryoda]

@GauranshMathur BTW: If PyQt6 is not yet available as distro package you can manually install it following these instructions (possible with some modifications if you are not using Ubuntu 22.04).

[GauranshMathur]

Hi, @aryoda ,

I was able to use your method via the PR work and am able to now run the program in debug mode in qt6, thanks for the tip. But i am having an issue with trying to recreate the problem.

I believe the steps to recreate the problem would be :

1. Run app.py in qt folder via the --debug tag
2. Create a local snapshot that you load
3. Do the following stated steps above to quickly create a snapshot stop restart and pause to see the issue

But I am having an issue on step 2 where this is the debug message I was getting:

DEBUG: [common/config.py:1689 Config._cron_line] Profile: test | Automatic backup: 0 cron_lines=['@reboot /usr/bin/nice -n19 /usr/bin/ionice -c2 -n7 /home/arkhaya/work/backintime/common/backintime --debug backup-job >/dev/null', ''] Traceback (most recent call last): File "/home/arkhaya/work/backintime/qt/settingsdialog.py", line 2355, in accept if self.validate(): File "/home/arkhaya/work/backintime/qt/settingsdialog.py", line 2001, in validate if not self.config.setupCron(): File "/home/arkhaya/work/backintime/common/config.py", line 1629, in setupCron crontab_lines = schedule.append_bit_to_crontab( TypeError: append_bit_to_crontab() missing 1 required positional argument: 'bit_lines'

[buhtz]

That was a Bug introduced by me. But is fixes by a PR I merged yesterday. So just get the latest state from this upstream repo.

EDIT: And be aware that it need to be a slow machine, like a RasperryPi. I am assuming that the bug is not reproducible on a machine with regular performance.