Day: July 6, 2016

Linux tib bits…

Linux tib bits…


Linux Networking Devices

Udev naming

There a few network gotchas when adding a new network card or copying VMs. The issue starts when an existing the name of the network adapter changes (e.g., from eth0 to eth1) network adapter’s MAC address changes because a configuration script in linux associates the name of the network adapter with its MAC address. It can be disabled:

Disable udev persistent net generation

echo -n > /etc/udev/rules.d/70-persistent-net.rules
echo -n > /lib/udev/rules.d/75-persistent-net-generator.rules

# disable udev persistent net generation

echo -n > /etc/udev/rules.d/70-persistent-net.rules
echo -n > /etc/udev/rules.d/75-persistent-net-generator.rules

Systemd naming

With systemd, network devices are named differently(ie. enp0s0 or wlp2s0). Although this provides a more consistence naming convention with network adapters in linux, in some cases, The old style naming is sometimes needed for environments or scripts. To fix that, In grub:


title Gentoo Linux 4.4.1
root (hd0,0)
kernel /kernel-genkernel-x86_64-4.4.9-gentoo root=ZFS dozfs init=/usr/lib/systemd/systemd
initrd /initramfs-genkernel-x86_64-4.4.9-gentoo


title Gentoo Linux 4.4.1
root (hd0,0)
kernel /kernel-genkernel-x86_64-4.4.9-gentoo root=ZFS dozfs init=/usr/lib/systemd/systemd net.ifnames=0
initrd /initramfs-genkernel-x86_64-4.4.9-gentoo

Magic SysReq

I have gotten into situations where the subsystems or subproccesses on a running system maybe not be performing as expected. If you ever need to reboot the host and its not connected to an pdu magic SysReq is the next best options.

You can activate it by:

echo 1 > /proc/sys/kernel/sysrq

If you need to reboot the host:

echo b > /proc/sysrq-trigger

Note: This will cause the kernel to send an instruction to the cpu to reset and it will not show down any processes cleanly and the same goes to the filesystem. USE WITH CAUTION!

To make it permanently turn on:

echo “kernel.sysrq = 1” » /etc/sysctl.conf

More infromation can be found: If you would like to learn more about magic SysRq you can read the sysrq.txt file in the kernel documentation.

Simple useful Python Function

Simple useful Python Function

These are functions that I have been useful and flexible to me.

import sys
import subprocess
import string
import socket
import re
import syslog
import smtplib
import os
import sys, getopt
from optparse import OptionParser

# Function that does basic standard output
def message(message):

#Get command line options then return the variables to be used in other parts of the script.
def CliOptions():
    Setup command-line parsing options
    parser = OptionParser()
    parser.add_option('-o', '--output', default = '',    dest = 'output', help = 'Where to output the file to.')
    parser.add_option('-i', '--input',  default = '',    dest = 'input',  help = 'The Input file.')
    parser.add_option('--TrueOrFalse',	default = False, dest = 'TOF', help = 'True or false value.')
    return parser.parse_args()

#Take the contents of data and write it in a file.
def WriteFile(outputFile, outputInformation): 
    fileHandle = open(outputFile + ".out", "w")
#Read a file and remove newline and return charaters. Then return the data back.
def readFileFunction(inputFile):
    InputFromFile = []
    with open(inputFile, "r") as ins:
        for inputFileLineItem in ins:
    return InputFromFile

#Have it output to syslog
def MsgLogging(msg):
	syslog.syslog(syslog.LOG_INFO, msg)

#This function calls shell commands. Clean the output but removing the any newline and return charaters using lambda.
def ExternalCommands(command):
    p1 = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    results = p1.stdout.readlines()

    resultsFromPopen = map(lambda s: s.rstrip('\r\n'), results)
    return resultsFromPopen

How to use the above functions:

#The messaging function:
message ("Hello World\n")

#For the CliOptions function, The function gets called, it getting the commandline arguments. The function will return data into an array.
(options,args) = CliOptions()

#For the msgLogging
MsgLogging("Hello World")

#For ExternalCommands
results = ExternalCommands("ls /")

#For readFileFunction
results = readFileFunction(pathToFile)

#For WriteFile
WriteFile("/tmp/test.txt", "Hello World")
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