Sudo Full Practical Session

Introduction Before we proceed, it would be best to cover some basic user administration topics that will be very useful in later chapters. Adding Users One of the most important activities in administering a Linux box is the addition of users. Here you'll find some simple examples to provide a...

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Using chkconfig to Start Daemons at Each runlevel

As stated earlier, the chkconfig command can be used to adjust which applications start at each runlevel. You can use this command with the --list switch to get a full listing of packages listed in /etc/init.d and the runlevels at which they will be on or off: ...

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Basic's of Networking

1. Define Network? A network is a set of devices connected by physical media links. A network is recursively is a connection of two or more nodes by a physical link or two or more networks connected by one or more nodes. 2. What is a Link? At the lowest level, a network can consist of two or more...

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Linux / Unix Commands For Connecting To The Serial Console

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...

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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. Task: Display Detected System's Serial Support Simple run dmesg command ...

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Troubleshooting Disk and Data store Related Issues  SHOOT:2

SHOOT: 2 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...

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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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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...

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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...

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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      ...

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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. 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...

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Redhat Enterprise Linux 5 / CentOS 5 monitor and track TCP connections on the network

Q. How do I track and monitor connection for eth1 public network interface under Redhat Enterprise Linux (RHEL) 5 server? Ans.You can use netstat command or tcptrack command. Both command can show established TCP connection and provides the ability to monitor the same....

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BASIC LDAP CONFIGURATION For RHEL / Centos / Fedora

INTRO: LDAP stands for Lightweight Directory Access Protocol. It is used as centralized data (or Directory) server (not database server) for various purposes. There is a difference between Directory server and a Database server. In Directory server the data is read more frequently than it is written. In Database server the data is written more frequently than it is read. Here we shall see how LDAP is used for creating centralized...

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Linux: Iptables Examples For New SysAdmins Part -->3

Before see this post please read my previous post (Linux: Iptables Examples For New SysAdmins Part -->2) #12: Log and Drop Packets   Type the following to log and block IP spoofing on public interface called eth1 # iptables -A INPUT -i eth1 -s 10.0.0.0/8 -j LOG --log-prefix "IP_SPOOF A: # iptables -A INPUT -i eth1 -s 10.0.0.0/8 -j DROP ...

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Linux: Iptables Examples For New SysAdmins Part -->2

Before see this post please read my previous post (Linux: Iptables Examples For New SysAdmins Part -->1) #3: Delete Firewall Rules To display line number along with other information for existing rules, enter: # iptables -L INPUT  -n --line-numbers # iptables -L OUTPUT -n --line-numbers # iptables...

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Linux: Iptables Examples For New SysAdmins Part -->1

Linux comes with a host based firewall called Netfilter. According to the official project site: netfilter is a set of hooks inside the Linux kernel that allows kernel modules to register callback functions with the network stack. A registered callback function is then called back for every packet that traverses the respective hook within the network stack. This Linux based firewall is controlled by the program called iptables to...

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Redhat / CentOS Iptables Firewall Configuration

H ow do I configure a host-based firewall called Netfilter (iptables) under CentOS / RHEL / Fedora / Redhat Enterprise Linux? Icon reference for Firewall Netfilter is a host-based firewall for Linux operating systems. It is included as part of the Linux distribution and it is activated...

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What is sysctl.conf in Linux

sysctl is an interface that allows you to make changes to a running Linux kernel. With /etc/sysctl.conf you can configure various Linux networking and system settings such as: 1.      Limit network-transmitted configuration for IPv4 2.      Limit network-transmitted configuration for IPv6 3.      Turn on execshield protection 4.      Prevent...

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