Wait until able to connect

while ! nc -w5 -z 10.0.0.100 22; do echo "hello"; done

Log executed command

14:27 $ (set -x; sleep 1 && sleep 2)
+ sleep 1
+ sleep 2

Check and modify connection mtu

To check:

[root@lxd-node3 ~]# netstat -i
Kernel Interface table
Iface             MTU    RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
ens10            1450      455      0      0 0           671      0      0      0 BMRU
eth0             1500       28      0      0 0            32      0      0      0 BMRU
lo              65536        0      0      0 0             0      0      0      0 LRU

Modify temporarily:

ifconfig eth0 mtu 1450

Permanently: edit /etc/sysconfig/network-scripts/ifcfg-eth0 file and add:

MTU=1450

lxd: Fix version in snap

 snap refresh lxd --channel=3.18

fedora: Lockdown a kernel version

Fedora typically keeps 3 latest kernel versions. However, what if you want to keep an old specific kernel version which is known to work well with your system? First, we need to install a dnf plugin that allows us to keep a specific version of any package:

sudo dnf install python3-dnf-plugins-extras-versionlock

Lets find all available kernel versions for your system:

sudo dnf list kernel --showduplicates

Install that specific version of the kernel:

sudo dnf install kernel-5.3.7-301.fc31

And lock it:

sudo dnf versionlock add kernel-5.3.7-301.fc31

To remove the lock:

sudo dnf versionlock delete kernel-5.3.7-301.fc31

Dell Precision 5540 - Battery drains in sleep mode

Run the following command to check the suspend mode:

cat /sys/power/mem_sleep 

If the output looks like this:

[s2idle] deep

It means that very inefficient suspend mode is active (drains battery from 100% to 0 in 9 hours). To enable "deep" mode, edit file /etc/default/grub and append "mem_sleep_default=deep" to GRUB_CMDLINE_LINUX:

GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="rd.lvm.lv=fedora/root rd.lvm.lv=fedora/swap rhgb quiet mem_sleep_default=deep"
GRUB_DISABLE_RECOVERY="true"
GRUB_ENABLE_BLSCFG=true

Apply changes:

sudo grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg

Restart your laptop and verify changes:

$ cat /sys/power/mem_sleep 
s2idle [deep]

Increase storage of a lxd container

By default lxd stopped to assign root (disk) device to a container. To modify storage volume of a container add a device like this:

lxc config device add surflyc root disk pool=default path=/ size=15GB

Restart the container to apply changes.

Log quireis in dnsmasq

Add the following line to dnsmasq configuration file: log-queries

Lxd on Fedora 31

Fedora 31 has started to use cgroups v2 by default. According to Common F31 bugs it doesn't play nice with Docker, lxd and others. To make fedora switch back to the old cgroups:

sudo grubby --update-kernel=ALL --args="systemd.unified_cgroup_hierarchy=0"

How to regenerate grub configuration

sudo grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg

wifi utils

List used wifi frequences

sudo iwlist wlp1s0 scan | grep Frequency | sort | uniq -c | sort -n

List available channels

iwlist channel

List wifi networks

nmcli d wifi

Fix isort in vscode for python2

Go to the vscode Python extension folder:

cd ~/.vscode/extensions/ms-python.python-2019.9.34911

Install latest version that is known to work with python 2:

pip2 install -t ./pythonFiles/lib/python --upgrade isort==4.3.17

python: Django-like testrunner

Django-like testrunner for non-django projects:

#!/usr/bin/env python

import argparse
import collections
import unittest
import sys


def main():
    parser = argparse.ArgumentParser(description='Django-like testrunner')
    parser.add_argument('specific_test', metavar='', type=str, nargs='?', help='Specifc test')
    parser.add_argument("--failfast", action="store_true")
    parser.add_argument("--verbosity", type=int, default=1)

    args = parser.parse_args()

    loader = unittest.TestLoader()
    all_tests = loader.discover('.', top_level_dir="./")
    suite = unittest.TestSuite()

    if args.specific_test:

        def walk_tests(tests):
            if isinstance(tests, collections.Iterable):
                for item in tests:
                    walk_tests(item)
                return
            if tests.id().startswith(args.specific_test):
                suite.addTest(tests)
            elif not str(tests).startswith("test"):
                sys.exit("Error in file %s" % tests)

        walk_tests(all_tests)
    else:
        suite.addTests(all_tests)

    unittest.TextTestRunner(verbosity=args.verbosity, failfast=args.failfast).run(suite)


if __name__ == "__main__":
    main()

fedora: SSL certificate viewer

GUI to view certificate:

gcr-viewer cert.pem

linux: List all IP addresses in a network

To list ip addresses of all connected to the network devices, use this command:

nmap -sn 192.168.0.0/24