Most embedded Linux /
BSD systems such as routers, servers and nas devices comes with console
interface (serial port with RS-232). BIOS can use this, and after boot BIOS
screen I/O is redirected so that you can use the device. RS-232 is also used
for communicating to headless server, where no monitor or keyboard is
installed, during boot when operating system is not running yet and therefore
no network connection is possible. You need to use a serial cable between your
computer and embedded system or server. In this post I will cover five common
utilities used for serial communication under Linux / Unix / *BSD and Mac OS X.
Friday, September 21, 2012
How To Check and Use Serial Ports Under Linux
How do I check and configure serial ports under
Linux for various purposes such as modem, connecting null modems or connect a
dumb terminal?
Linux offers various tools. Linux uses ttySx for a serial port device name. For example, COM1 (DOS/Windows name) is ttyS0, COM2 is ttyS1 and so on.
Linux offers various tools. Linux uses ttySx for a serial port device name. For example, COM1 (DOS/Windows name) is ttyS0, COM2 is ttyS1 and so on.
Task:
Display Detected System's Serial Support
Simple
run dmesg command
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Tuesday, September 18, 2012
Troubleshooting Disk and Data store Related Issues SHOOT:2
SHOOT: 2
VMFS Lock Volume is Corrupted
VMFS Lock Volume is Corrupted
Details
You
may observe the following events within the /var/log/vmkernel logs within your
VMware ESX host:
Volume
4976b16c-bd394790-6fd8-00215aaf0626 (san-lun-100) may be damaged on disk.
Corrupt lock detected at offset 0
Note:
In this example 4976b16c-bd394790-6fd8-00215aaf0626 represents the UUID of the
VMFS datastore and san-lun-100 represents the name of the VMFS datastore.
You
may observe the following events within the /var/log/vmkernel logs within your
VMware ESX host:
Resource
cluster metadata corruption detected Volume 4976b16c-bd394790-6fd8-00215aaf0626
(san-lun-100) may be damaged on disk.
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Troubleshooting Disk and Data store Related Issues SHOOT:1
SHOOT: 1
Troubleshooting
a VMFS resource volume that is corrupted
The
event indicates the reported VMFS volume is corrupted.
Example
If
4976b16c-bd394790-6fd8-00215aaf0626 represents the UUID and san-lun-100
represents the associated volume label, you see:
For
Event: vmfs.lock.corruptondisk
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Wednesday, September 12, 2012
Allow A Normal User To Run Commands As root Under Linux / UNIX Operating Systems
From my mail bag:
I would like to run
few commands such as stop or start web server as a root user. How do I allow a
normal user to run these commands as root?
You need to use the sudo command which is use to execute a command as another
user. It allows a permitted user to execute a command as the superuser or
another user, as specified in the /etc/sudoers (config file that defines or
list of who can run what) file. The sudo command allows users to do tasks on a
Linux system as another user.
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Wednesday, September 5, 2012
Shell Script To Encrypt Any Given Text File
In cryptography, encryption is the process of
transforming information (referred to as plaintext) using an algorithm (called
cipher) to make it unreadable to anyone except those possessing special
knowledge, usually referred to as a key.
Mcrypt is a
simple crypting program, a replacement for the old unix crypt. When
encrypting or decrypting a file, a new file is created with the extension .nc
and mode 0600. The new file keeps the modification date of the original. The
original file may be deleted by specifying the -u parameter. If no files are
specified, the standard input is encrypted to the standard output.
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Shell Script List All Top IP Address Accessing Apache Web Server
********************************
#!/bin/bash
# Shell Script To
List All Top Hitting IP Address to your webserver.
# This may be
useful to catch spammers and scrappers.
# where to store
final report?
DEST=/var/www/reports/ips
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Basic of Shell Script
What Is a Shell?
Ø The shell is a user
program or it is an environment provided for user interaction.
Ø It is a command language
interpreter that executes commands read from the standard input device such as
keyboard or from a file.
Ø The shell gets started
when you log in or open a console (terminal).
Ø Quick and dirty way to
execute utilities.
Ø The shell is not part of
system kernel, but uses the
system kernel to execute programs, create files etc.
Ø Several shells are
available for Linux including:
Ø BASH ( Bourne-Again
SHell ) - Most common shell in
Linux. It's Open Source.
Ø CSH (C SHell) - The C shell's syntax and
usage are very similar to the C programming language.
Ø KSH (Korn SHell) - Created by David Korn at AT
& T Bell
Labs. The Korn Shell also was the base for the POSIX Shell standard
specifications.
Ø TCSH - It is an enhanced but completely
compatible version of the Berkeley UNIX C shell (CSH).
Please note
that each shell does the same job, but each understands different command
syntax and provides different built-in functions. Under MS-DOS, the shell name is COMMAND.COM which is also used for the same
purpose, but it is by far not as powerful as our Linux Shells are!
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Linux log files location and how do I view logs files?
Q. I am new to Linux and I would like to know
where are the log files located under Debian or Cento OS Linux server? How do I
open or view log files?
Ans. Almost all logfiles are located under /var/log directory (and subdirectory). You can change to this directory using cd command but you need to be the root user. You can use less, more, cat or tail command to see the logs.
Ans. Almost all logfiles are located under /var/log directory (and subdirectory). You can change to this directory using cd command but you need to be the root user. You can use less, more, cat or tail command to see the logs.
Go to /var/logs
directory:
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How do I rotate log files?
Q. How do I rotate log files under Linux operating system?
A. You need use tool called logrotate, which is
designed to ease administration of systems that generate large numbers of log
files. It allows automatic rotation, compression, removal, and mailing of log
files.
Each
log file may be handled daily, weekly, monthly, or when it grows too large.
With this tool you keep logs longer with less disk space.
Default configuration file
The default configuration file is
/etc/logrotate.conf:
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