Unix

Uname command with examples

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1. uname command

The uname command prints information about the system. uname is a portmanteau word made up from "unix" and "name". uname can be called from the command line in Linux as,

uname [OPTION]...

The most common way to use uname is with the -a option, which stands for "all" the information.… Read more

Syslog

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1.0 Syslog

Syslog is a protocol for conveying event notification messages.

Syslog was first developed by Eric Allman for logging as a part of the Sendmail project in the 1980s. It soon became a de-facto standard for logging on Unix-like systems.… Read more

POSIX Shared Memory in Linux

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1.0 Shared Memory

Shared memory is the fastest method of interprocess communication (IPC) under Linux and other Unix-like systems. The system provides a shared memory segment which the calling process can map to its address space. After that, it behaves just like any other part of the process's address space.… Read more

POSIX Semaphores in Linux

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1.0 Semaphores

Semaphores are used for process and thread synchronization. Semaphores are clubbed with message queues and shared memory under the Interprocess Communication (IPC) facilities in Unix-like systems such as Linux. There are two varieties of semaphores, the traditional System V semaphores and the newer POSIX semaphores.… Read more

Tiger

Awk Tutorial

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1.0 awk

awk is a filter which takes the input and gives output after matching desired patterns and doing processing linked to matched patterns. awk is well suited for processing voluminous raw text data and producing statistical reports from it.

awk is named after the first character of the names of its designers, Al Aho, Peter Weinberger and Brian Kernighan, who developed it for Unix systems in the 1970s.… Read more

Sed command in Linux

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1.0 sed

sed is a stream editor that accepts a list of commands and input file names. It applies the commands one by one on each line of input and writes the resulting lines on the standard output. The commands are separated by newlines.… Read more

grep Command in Linux

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1.0 grep

grep is a program for searching a given string pattern in files. It searches the files for the pattern and prints the lines that contain strings matching the pattern. For example,

$ # grep pattern filenames ... 
$ grep 'hbox' find.c
… Read more
bc

Trigonometric calculations with bc

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bc, the basic calculator under Linux and UNIX environments, provides commands for doing arbitrary precision mathematical calculations. The syntax for basic arithmetic functions is intuitive. Here, we look at the commands for doing trigonometric calculations.

Scale

The global scale variable gives the number of digits after the decimal point.… Read more

iostat

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The iostat command is for getting the CPU and input-output devices' statistics for Linux and Unix systems. For example,

$ iostat
Linux 3.0.0-14-generic (hostname) 	Wednesday 06 June 2012 	_i686_	(2 CPU)  

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          17.38    0.13    3.13    1.63    0.00   77.74

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda              11.78       111.65        69.79   11663838    7290650

The above output has two reports, the CPU utilization report and the device utilization report.… Read more

top command

top Command in Linux

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The Unix top command is useful for monitoring systems continuously for processes that take more system resources like the CPU time and the memory. top periodically updates the display showing the high resource consuming processes at the top. top is an excellent aid in checking a system.… Read more