Count all http response status codes in a web application log files on linux

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Count all http response status codes in a web application log files on linux

Here is one way to count all the HTTP response status codes in a web application log file on Linux:

  1. Open the log file using the cat command:
cat log_file
  1. Use the grep command to search for lines that contain an HTTP status code:
cat log_file | grep -Eo 'HTTP/[0-9\.]+ [0-9]+'

This will output all the lines in the log file that contain an HTTP status code.

  1. Use the awk command to extract the status code from each line:
cat log_file | grep -Eo 'HTTP/[0-9\.]+ [0-9]+' | awk '{print $2}'

This will output a list of all the status codes in the log file.

  1. Use the sort and uniq commands to count the number of occurrences of each status code:
cat log_file | grep -Eo 'HTTP/[0-9\.]+ [0-9]+' | awk '{print $2}' | sort | uniq -c

1- Sample Log file:

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Given the log file below, we want to know all http response status code and sort them from the highest amount of response code to the lowest.

2- Use this command below to Count all http response status codes in a web application log files on linux:





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awk '{print $9}' sample_log.log | sort | uniq -c | sort -rn

3- Output

Count Each unique Response Status Code from Web App log file

Learn more about http response status code here

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Basic Gotcha Linux Questions for IT DevOps and SysAdmin Interviews

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Some IT DevOps, SysAdmin, Developer positions require the knowledge of basic linux Operating System. Most of the time, we know the answer but forget them when we don’t practice very often. This refresher will help you prepare for the linux portion of your IT interview by answering some gotcha Linux Questions for IT DevOps and SysAdmin Interviews.

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Latest Linux Feeds

I- Networking:

  1. How many bytes are there in a MAC address?
    48.
    MAC, Media Access Control, address is a globally unique identifier assigned to network devices, and therefore it is often referred to as hardware or physical address. MAC addresses are 6-byte (48-bits) in length, and are written in MM:MM:MM:SS:SS:SS format.
  2. What are the different parts of a TCP packet?
    The term TCP packet appears in both informal and formal usage, whereas in more precise terminology segment refers to the TCP protocol data unit (PDU), datagram to the IP PDU, and frame to the data link layer PDU: … A TCP segment consists of a segment header and a data section.
  3. Networking: Which command is used to initialize an interface, assign IP address, etc.
    ifconfig (interface configuration). The equivalent command for Dos is ipconfig.
    Other useful networking commands are: Ping, traceroute, netstat, dig, nslookup, route, lsof
  4. What’s the difference between TCP and UDP; Between DNS TCP and UDP?
    There are two types of Internet Protocol (IP) traffic. They are TCP or Transmission Control Protocol and UDP or User Datagram Protocol. TCP is connection oriented – once a connection is established, data can be sent bidirectional. UDP is a simpler, connectionless Internet protocol.
    The reality is that DNS queries can also use TCP port 53 if UDP port 53 is not accepted.
    DNS uses TCP for Zone Transfer over port :53.
    DNS uses UDP for DNS Queries over port :53.

  5. What are defaults ports used by http, telnet, ftp, smtp, dns, , snmp, squid?
    All those services are part of the Application level of the TCP/IP protocol.
    http => 80
    telnet => 23
    ftp => 20 (data transfer), 21 (Connection established)
    smtp => 25
    dns => 53
    snmp => 161
    dhcp => 67 (server), 68 (Client)
    ssh => 22
    squid => 3128
  6. How many host available in a subnet (Class B and C Networks)
  7. How DNS works?
    When you enter a URL into your Web browser, your DNS server uses its resources to resolve the name into the IP address for the appropriate Web server.
  8. What is the difference between class A, class B and class C IP addresses?
    Class A Network (/ 8 Prefixes)
    This network is 8-bit network prefix. IP address range from 0.0.0.0 to 127.255.255.255
    Class B Networks (/16 Prefixes)
    This network is 16-bit network prefix. IP address range from 128.0.0.0 to 191.255.255.255Class C Networks (/24 Prefixes)
    This network is 24-bit network prefix.IP address range from 192.0.0.0 to 223.255.255.255
  9. Difference between ospf and bgp?
    The first reason is that BGP is more scalable than OSPF. , and this, normal igp like ospf cannot perform. Generally speaking OSPF and BGP are routing protocols for two different things. OSPF is an IGP (Interior Gateway Protocol) and is used internally within a companies network to provide routing.

II- Operating System
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  1. How to find the Operating System version?
    $uname -a
    To check the distribution for redhat for example: $cat /etc/redhat –release
  2. How to list all the process running?
    top
    To list java processes, ps -ef | grep java
    To list processes on a specific port:
    netstat -aon | findstr :port_number
    lsof -i:80
  3. How to check disk space?
    df shows the amount of disk space used and available.
    du displays the amount of disk used by the specified files and for each subdirectories.
    To drill down and find out which file is filling up a drive: du -ks /drive_name/* | sort -nr | head
  4. How to check memory usage?
    free or cat /proc/meminfo
  5. What is the load average?
    It is the average sum of the number of process waiting in the queue and the number of process currently executing over the period of 1, 5 and 15 minutes. Use top to find the load average.
  6. What is a load balancer?
    A load balancer is a device that acts as a reverse proxy and distributes network or application traffic across a number of servers. Load balancers are used to increase capacity (concurrent users) and reliability of applications.
  7. What is the Linux Kernel?
    The Linux Kernel is a low-level systems software whose main role is to manage hardware resources for the user. It is also used to provide an interface for user-level interaction.
  8. What is the default kill signal?
    There are many different signals that can be sent (see signal for a full list), although the signals in which users are generally most interested are SIGTERM (“terminate”) and SIGKILL (“kill”). The default signal sent is SIGTERM.
    kill 1234
    kill -s TERM 1234
    kill -TERM 1234
    kill -15 1234
  9. Describe Linux boot process
    BIOS => MBR => GRUB => KERNEL => INIT => RUN LEVEL
    As power comes up, the BIOS (Basic Input/Output System) is given control and executes MBR (Master Boot Record). The MBR executes GRUB (Grand Unified Boot Loader). GRUB executes Kernel. Kernel executes /sbin/init. Init executes run level programs. Run level programs are executed from /etc/rc.d/rc*.d
    Mac OS X Boot Process:

    Boot ROMFirmware. Part of Hardware system
    BootROM firmware is activated
    POSTPower-On Self Test
    initializes some hardware interfaces and verifies that sufficient memory is available and in a good state.
    EFI Extensible Firmware Interface
    EFI does basic hardware initialization and selects which operating system to use.
    BOOTX boot.efi boot loader
    load the kernel environment
    Rooting/Kernel The init routine of the kernel is executed
    boot loader starts the kernel’s initialization procedure
    Various Mach/BSD data structures are initialized by the kernel.
    The I/O Kit is initialized.
    The kernel starts /sbin/mach_init
    Run Level mach_init starts /sbin/init
    init determines the runlevel, and runs /etc/rc.boot, which sets up the machine enough to run single-user.
    rc.boot figures out the type of boot (Multi-User, Safe, CD-ROM, Network etc.)
  10. List services enabled at a particular run level
    chkconfig –list | grep 5:0n
    Enable|Disable a service at a specific run level: chkconfig on|off –level 5
  11. How do you stop a bash fork bomb?
    Create a fork bomb by editing limits.conf:
    root hard nproc 512
    Drop a fork bomb as below:
    :(){ :|:& };:
    Assuming you have access to shell:
    kill -STOP
    killall -STOP -u user1
    killall -KILL -u user1
  12. What is a fork?
    fork is an operation whereby a process creates a copy of itself. It is usually a system call, implemented in the kernel. Fork is the primary (and historically, only) method of process creation on Unix-like operating systems.
  13. What is the D state?
    D state code means that process is in uninterruptible sleep, and that may mean different things but it is usually I/O.

III- File System

  1. What is umask?
    umask is “User File Creation Mask”, which determines the settings of a mask that controls which file permissions are set for files and directories when they are created.
  2. What is the role of the swap space?
    A swap space is a certain amount of space used by Linux to temporarily hold some programs that are running concurrently. This happens when RAM does not have enough memory to hold all programs that are executing.
  • What is the role of the swap space?
    A swap space is a certain amount of space used by Linux to temporarily hold some programs that are running concurrently. This happens when RAM does not have enough memory to hold all programs that are executing.
  • What is the null device in Linux?
    The null device is typically used for disposing of unwanted output streams of a process, or as a convenient empty file for input streams. This is usually done by redirection. The /dev/null device is a special file, not a directory, so one cannot move a whole file or directory into it with the Unix mv command.You might receive the “Bad file descriptor” error message if /dev/null has been deleted or overwritten. You can infer this cause when file system is reported as read-only at the time of booting through error messages, such as“/dev/null: Read-only filesystem” and “dup2: bad file descriptor”.
    In Unix and related computer operating systems, a file descriptor (FD, less frequently fildes) is an abstract indicator (handle) used to access a file or other input/output resource, such as a pipe or network socket.
  • What is a inode?
    The inode is a data structure in a Unix-style file system that describes a filesystem object such as a file or a directory. Each inode stores the attributes and disk block location(s) of the object’s data.

IV- Databases

  1. What is the difference between a document store and a relational database?
    In a relational database system you must define a schema before adding records to a database. The schema is the structure described in a formal language supported by the database and provides a blueprint for the tables in a database and the relationships between tables of data. Within a table, you need to define constraints in terms of rows and named columns as well as the type of data that can be stored in each column.In contrast, a document-oriented database contains documents, which are records that describe the data in the document, as well as the actual data. Documents can be as complex as you choose; you can use nested data to provide additional sub-categories of information about your object. You can also use one or more document to represent a real-world object.
  2. How to optimise a slow DB?
    • Rewrite the queries
    • Change indexing strategy
    • Change schema
    • Use an external cache
    • Server tuning and beyond
  3. How would you build a 1 Petabyte storage with commodity hardware?
    Using JBODs with large capacity disks with Linux in a distributed storage system stacking nodes until 1PB is reached.
    JBOD (which stands for “just a bunch of disks”) generally refers to a collection of hard disks that have not been configured to act as a redundant array of independent disks (RAID) array.
    JBOD

V- Scripting


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  1. What is @INC in Perl?
    The @INC Array. @INC is a special Perl variable that is the equivalent to the shell’s PATH variable. Whereas PATH contains a list of directories to search for executables, @INC contains a list of directories from which Perl modules and libraries can be loaded.
  2. Strings comparison – operator – for loop – if statement
  3. Sort access log file by http Response Codes
    Via Shell using linux commands
    cat sample_log.log | cut -d ‘”‘ -f3 | cut -d ‘ ‘ -f2 | sort | uniq -c | sort -rn
  4. Sort access log file by http Response Codes Using awk
    awk ‘{print $9}’ sample_log.log | sort | uniq -c | sort -rn
  5. Find broken links from access log file
    awk ‘($9 ~ /404/)’ sample_log.log | awk ‘{print $7}’ sample_log.log | sort | uniq -c | sort -rn
  6. Most requested page:
    awk -F\” ‘{print $2}’ sample_log.log | awk ‘{print $2}’ | sort | uniq -c | sort -r
  7. Count all occurrences of a word in a file
    grep -o “user” sample_log.log | wc -w

Learn more at http://career.guru99.com/top-50-linux-interview-questions/

Real Time Linux Jobs

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How to pipe grep on command line on windows and Linux

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How to pipe grep on command line on Windows and Linux?

Let’s find how to pipe grep or find a specific string after running a command using shell, batch and powershell (windows and Linux)

  • On Linux via shell

    ls -al | grep filename

  • On Windows via powershell

    GetChildItem | Select-Object “filename”
    or
    GetChildItem | where-Object {$_ -match “filename”}

  • On Windows via batch

    Dir | findstr “filename”

On both Windows and Linux, you can use the grep command in combination with the | (pipe) operator to filter the output of another command. The | operator takes the output of the command on the left and passes it as input to the command on the right.

Here is an example of how to use the grep command with the | operator on both Windows and Linux:

On Linux:

# List all the files in the current directory and filter the output to show only the files that contain the word "example"
ls | grep example

On Windows:

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# List all the files in the current directory and filter the output to show only the files that contain the word "example"
dir | findstr example

In this example, the ls (Linux) or dir (Windows) command lists all the files in the current directory, and the grep (Linux) or findstr (Windows) command filters the output to show only the lines that contain the word “example”.

You can use the grep command with the | operator in combination with other command-line utilities to perform various tasks. For example, you can use the grep command to filter the output of the ps command to show only the processes that contain a particular string in their command line arguments.

# Show all the processes that contain the string "python" in their command line arguments
ps -aux | grep python

I hope this helps! Let me know if you have any questions.


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reverse a string on Linux and Windows

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How to reverse a string on Linux and Windows

On Linux:

  1. Using the rev command: The rev command is a utility that reverses the lines of a file or the characters in a string. To reverse a string, you can use the echo command to pass the string to rev:
echo "string" | rev
  1. Using the sed command: The sed command is a powerful utility that can perform various text transformations. To reverse a string, you can use the sed command with the -r option and the 's/.*(.)/\1/g' expression:
echo "string" | sed -r 's/.*(.)/\1/g'
  1. Using the awk command: The awk command is a programming language that is used for text processing. To reverse a string, you can use the awk command with the {print} action:
echo "string" | awk '{print $1}'

On Windows:

  1. Using the powershell command: The powershell command is a shell that provides a command-line interface for Windows. To reverse a string, you can use the powershell command with the -C option and the '[System.Text.Encoding]::Unicode.GetString([System.Text.Encoding]::Unicode.GetBytes("string"))' expression:
powershell -C "[System.Text.Encoding]::Unicode.GetString([System.Text.Encoding]::Unicode.GetBytes("string"))"
  1. Using the cmd command: The cmd command is the command-line interpreter for Windows. To reverse a string, you can use the cmd command with the for loop:
cmd /c "for /L %i in (1,1,%len%) do @echo !string:~%len%-%i,1!"

These are some ways to reverse a string on Linux and Windows. There are other ways to achieve this, using different utilities or programming languages.

Via shell script on Linux

reverse a string on Linux and Windows

sh-3.2# vi reverse.sh
#### Start Script #####
#!/bin/bash
input_string=”$1″
reverse_string=””

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input_string_length=${#input_string}
for (( i=$input_string_length-1; i>=0; i– ))
do
reverse_string=”$reverse_string${input_string:$i:1}”
done

echo “$reverse_string”
##### End Script #####

Let’s run it:


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sh-3.2# chmod 775 reverse.sh
sh-3.2# ./reverse.sh Etienne
enneitE

Via powershell script on Windows

#Let’s use the script reverse.ps1 below.
######
$string=”Etienne”
$string_array=$string -split “”
[array]::Reverse($string_array)
$string_array -join ”

#####Output#####
PS C:\Users\etienne_noumen\Documents\Etienne\Scripting> .\reverse.ps1

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E t i e n n e

enneitE

Via powershell script on Windows in one line

([regex]::Matches($String,’.’,’RightToLeft’) | ForEach {$_.value}) -join ”

Via batch script on Windows

::Note: ReverseStr also calls StrLen
::and string length is not greater than 80 chars
:: but can be changed.

@echo off
SetLocal EnableDelayedExpansion
cls
set Str=Etienne
call :StrLen %Str%
echo Length=%Len%
call :ReverseStr %Str%
echo String=%Str%
echo Reverse Str=%Reverse%
exit /b

::—————-
:: Calc Var Length
::—————-
:: %*=Str to Check
:: Returns %Len%
:: —————
:StrLen %*
set Data=%*
for /L %%a in (0,1,80) do (
set Char=!Data:~%%a,1!
if not “!Char!”==”” (
set /a Len=%%a+1
) else (exit /b)
)
exit /b

::—————
:: Reverse String
::—————
:: %* Str to Reverse
:: Returns %Reverse%
::——————
:ReverseStr %*
set Data=%*
call :StrLen %Data%
for /L %%a in (!Len!,-1,0) do (
set Char=!Data:~%%a,1!
set Reverse=!Reverse!!Char!
)
exit /b

Via perl script on Windows or Linux

Via python script on Windows or Linux

def reverse_string(a_string)
return a_string[::-1]
reverse_string(“etienne”) returns “enneite”
Source:

  1. http://www.computing.net/answers/programming/reverse-a-string-in-dos/26004.html

Mac OS X Boot Process

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What is Mac OS X Boot Process:

The Mac OS X boot process involves several stages, in which the operating system performs various tasks to prepare the system for use.

  1. When the Mac is powered on, the firmware (a low-level software that controls the hardware) performs a power-on self-test (POST) to check the hardware components.
  2. The firmware loads the bootloader, which is responsible for loading the operating system kernel and transferring control to it. In Mac OS X, the bootloader is called the boot.efi file.
  3. The operating system kernel, which is the core of the operating system, initializes the system and starts the system services.
  4. The system services, such as the device drivers, are loaded and initialized.
  5. The operating system loads the user profile and starts the user interface, such as the desktop or the login screen.
  6. The user can log in and start using the system.

This is a general overview of the Mac OS X boot process. The exact sequence of events may vary depending on the specific version of Mac OS X and the hardware configuration of the system.

Boot ROMFirmware. Part of Hardware system
BootROM firmware is activated
POSTPower-On Self Test
initializes some hardware interfaces and verifies that sufficient memory is available and in a good state.
EFI Extensible Firmware Interface
EFI does basic hardware initialization and selects which operating system to use.
BOOTX boot.efi boot loader
load the kernel environment
Rooting/Kernel The init routine of the kernel is executed
boot loader starts the kernel’s initialization procedure
Various Mach/BSD data structures are initialized by the kernel.
The I/O Kit is initialized.
The kernel starts /sbin/mach_init
Run Level mach_init starts /sbin/init
init determines the runlevel, and runs /etc/rc.boot, which sets up the machine enough to run single-user.
rc.boot figures out the type of boot (Multi-User, Safe, CD-ROM, Network etc.)




    • Power is turned on.
    • Open Firmware code is executed.
    • Hardware information is collected and hardware is initialized.
    • Something (usually the OS, but also things like the Apple Hardware Test, etc.) is selected to boot. The user may be prompted to select what to boot.
    • Control passes to /System/Library/CoreServices/BootX, the boot loader. BootX loads the kernel and also draws the OS badges, if any.
    • BootX tries to load a previously cached list of device drivers (created/updated by /usr/sbin/kextcache). Such a cache is of the type mkext and contains the info dictionaries and binary files for multiple kernel extensions. Note that if the mkext cache is corrupt or missing, BootX would look in /System/Library/Extensions for extensions that are needed in the current scenario (as determined by the value of the OSBundleRequired property in the Info.plist file of the extension’s bundle.
    • The init routine of the kernel is executed. The root device of the booting system is determined. At this point, Open Firmware is not accessible any more.
    • Various Mach/BSD data structures are initialized by the kernel.
    • The I/O Kit is initialized.
    • The kernel starts /sbin/mach_init, the Mach service naming (bootstrap) daemon. mach_init maintains mappings between service names and the Mach ports that provide access to those services.

From here on, the startup becomes user-level:

    • mach_init starts /sbin/init, the traditional BSD init process. init determines the runlevel, and runs /etc/rc.boot, which sets up the machine enough to run single-user.
    • rc.boot figures out the type of boot (Multi-User, Safe, CD-ROM, Network etc.). In case of a network boot (the sysctl variable kern.netboot will be set to 1 in which case), it runs /etc/rc.netboot with a start argument.

Source: http://osxbook.com/book/bonus/ancient/whatismacosx/arch_startup.html

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Linux Boot process

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Let’s describe Linux Boot Process:

The Linux boot process involves several stages, in which the operating system performs various tasks to prepare the system for use.

  1. When the system is powered on, the BIOS (Basic Input/Output System) or the UEFI (Unified Extensible Firmware Interface) performs a power-on self-test (POST) to check the hardware components and to load the bootloader.
  2. The bootloader, such as GRUB (GRand Unified Bootloader), is responsible for loading the operating system kernel and transferring control to it.
  3. The operating system kernel, which is the core of the operating system, initializes the system and starts the system services.
  4. The system services, such as the device drivers, are loaded and initialized.
  5. The operating system loads the user profile and starts the user interface, such as the desktop or the login screen.
  6. The user can log in and start using the system.

This is a general overview of the Linux boot process. The exact sequence of events may vary depending on the specific distribution of Linux and the hardware configuration of the system.

BIOSBasic INPUT/OUTPUT System.
Executes MBR
MBR Master Boot Record
Executes GRUB
GRUB Grand Unified Bootloader
Executes kernel
KERNEL Kernel
Executes /sbin/init
INIT Init
Executes Run level programs
Run Level Run Level Programs are executed from /etc/rc.d/rc*.d/
  • As power comes up the BIOS is given control
  • BIOS runs self tests, usually including cursory memory tests.
  • The BIOS then loads the first sector of the disk to be used for booting and transfers control to it.
  • The MBR code varies. One version will chain to the code in the first sector of the boot partition (Windows), another will load a bootloader. Windows boot proceeds from code and information in the boot partition.
  • The bootloader chooses kernel location and version
  • The bootloader prepares kernel and initrd image in memory, transfers control to kernel
  • Loading kernel modules
  • Discovering hardware and load additional kernel modules to support it
  • Looking for disks
  • R/O mount of / partition so that it can potentially be checked and repaired
  • init process spawn
  • /etc/inittab read and executing
  • Mounting all FSes from /etc/fstab
  • runlevels running (based on default runlevel in /etc/inittab) or another init method such as systemd or upstart
  • rc.local
  • login prompt

Source:

    1. http://unix.stackexchange.com/questions/27034/discribe-in-details-tha-boot-process-of-any-linux-system
    1. http://www.thegeekstuff.com/2011/02/linux-boot-process/
  1. Watch video here
  2. http://www.slideshare.net/dominiquec/understanding-the-boot-process
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