Amit's Blog (Page 2)

Build 32 bit application or libraries on 64 bit machine

In order to configure script to build 32bit library on a 64 bit machine, you would have to pass the following arguments : ./configure --build=i686-pc-linux-gnu "CFLAGS=-m32" "CXXFLAGS=-m32" "LDFLAGS=-m32" Also, If you get an error that says : configure: error: C++ compiler cannot

nagios

Nagios Bash script to monitor Domain Expiration

This little script here, lets you use nagios to monitor domain name expiration and warn you ahead of time. You can also use it to just run some cron jobs, our extract the portion you need and use in other places : !/bin/bash #Author : Amit K Nepal domain=$1 if

Resize Partition with parted

If you ever wanted to resize a partition to grow unfilled space, you can use parted to grow the partition size. parted /dev/sdx or parted /dev/mmcblk0 print Now note the size of the disk and the start of the partition that you want to resize. rm n=partition

Centos / Redhat 7 Switching back to iptables

It may be frustrating to learn yet another firewall (firewalld) in Centos or RHEL 7 . Here is how you can switch back to the favorite IPTABLES. Stop firewalld and disable it to start at boot time : systemctl stop firewalld systemctl disable firewalld Now Initiate and enable Iptables (IP V4 ) and

selinux

SELinux Tutorial

Selinux is Security Enhanced Linux. I see that many administrators disable Selinux to ease administration, however it is a good idea to enable SELINUX. View Selinux Status: getenforce Disable SELinux : setenforce 0 Disable SeLinux Per Process: Apache: semange permissive -a httpd_t View Associated Ports SELinux semanage port -l Some

Apache

New Apache : Authz_core:error Client Denied by Server Configuration

The newer version of apache 2.4.6 that comes with Centos 7, seems to require some additional statement. If you are using htaccess , then you have to add the following keyword in order to fix the issue : Require all granted

Postfix

Postfix - Sender address rejected: User unknown in virtual mailbox table

Sometimes you may want to be able to send email from non existent email addresses on your own networks for notification purposes, you may get error “Sender address rejected: User unknown in virtual mailbox table”. In order to over come this issue, you have to disable this option : “smtpd_reject_

packet capture

Filtering capture files with wire shark

Filter by IP address, source and or destination IP Address ip.addr192.168.1.1 ip.src192.168.1.1 ip.dst192.168.1.1 (ip.src 192.168.1.1)||(ip.dst192.168.1.1) (ip.src192.168.1.1)&&(ip.dst==192.168.1.1) To

Postfix

Postfix Spam Control

Reject / Discard / Redirect emails based on header checks : vi /etc/postfix/main.cf header_checks = regexp:/etc/postfix/header_checks vi /etc/postfix/header_checks /^From: "Mechanic/ REJECT /^To: someone@example.com/ REDIRECT someone@example2.com /^To [someone@example2.com/%5ETo]: [bademail@example.com/ REJECT /^Subject](mailto:bademail@example.

Postfix

Postfix Commands

View Postfix Version : postconf -d | grep mail_version postconf -d mail_version

Samba Share Fedora 20

Install required packages : yum install samba samba-common samba-client cups-lib system-config-samba Make a shared Directory : In my case, I did mount an external hard drive at /mnt/usbDrive , which I wanted to be able to share to my Home Network. mkdir /mnt/usbDrive && cd /mnt/ Now, configure SELINUX so

Mounting NTFS Filesystem

NTFS filesystem can be mounted on Linux systems by installing a kernel module that supports NTFS filesystem. A packate ntfs-3g can be used to installed such a module and ntfs utilities. yum install ntfs-3g If the repository cannot find the package, you might have to install epel repository. For Centos

ntp reflection attack

NTP Reflection Attack

In order to avoid NTP reflection attack , you need to disable the monlist command support or this can also be fixed by updating NTP to 4.2.7 vi /etc/ntp.conf restrict -4 default nomodify nopeer noquery notrap restrict -6 default nomodify nopeer noquery notrap # allow NTP messages from

vmware esxi

VMware ESXI packet capture

Packet capture for a port : tcpdump-uw -i vmk0 -s 1514 port 123 Increase the verbosity : tcpdump-uw -i vmk0 -s 1514 -vvv View traffic for a host : tcpdump-uw -i vmk0 -s 1514 host x.x.x.x Capture for specific port : tcpdump-uw -i vmk0 -s 1514 port not 21 and port

unzip

ZIP tips and tricks in Linux

View List of files inside a zip file: unzip -l filename.zip (list files ) Extract Single File from a zip file: unzip -j "archive.zip" "archive/filename.zip" -d .

qmail

Root Alias with Qmail

In order to create root alias , you have to edit the .qmail-root file on qmail server vi /var/qmail/alias/.qmail-root Now add the email address that you want to alias to and add & at the begining &sendto@domain.com [&sendto@domain.com]

Chrooting Users with SFTP

Prerequisite : OpenSSH 4.9p1 or newer is required, you can verify with the following command : Note : User can be added with /bin/false or /bin/bash if you want to allow shell access , for shell access refer to the bottom section as well. rpm -qa | grep -i openssh Match User

Iptables initial Configuration

Iptables Configuration*filter :INPUT ACCEPT [0:0] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [0:0] Block all other hackers and hacking attempts or exclusive block here -A INPUT –s x.x.x.x –j DROP Reject packets from RFC1918 class networks on your wan interface, which would mean spoofed Assumption

Log Messages with specific prefix to a separate file

With rsyslog you can log messages with specific prefix to a separate file. For example, if you wanted to put iptables log into a separate log file, with the syslog you have to live with log combined with kernel logs. In order to put the iptables log to a separate

Download RPM Packages with yum

Sometimes, it is desirable to download packages from yum repo.Here is how you can do that. Yum download only plugin is required. yum install yum-downloadonly After installing that plugin , you can download the packages as : yum install --downloadonly --downloaddir=/usr/local/src/

Email Server Utilities

To check for email report including SPF, Domain Keys , send a blank email to : check-auth@verifier.port25.com and wait for the reply with all the report.

Block Chinese Spam

Charsets from asia: /^Content-type:.charset\s=[\s"] (big5|euc-kr|gb2312|ks_c_5601-1987|ISO-2022-JP)/ REJECT /^Subject:.[Big5]./ REJECT /^Subject: =?iso-8859-1./ REJECT

PHP

Php Display only number of characters from string

This is an example to display only 13 characters from a string: $string = (strlen($string) > 13) ? substr($string,0,10).'...' : $string;

PHP

Execute Windows Batch File from php

If you ever needed to execute a batch file from php, you run it as : system ("cmd /c C:/path-to/file.bat");

windows scripting

Terminating a windows process with a Batch File

You might come acrosss a situation where you would want to terminate a process with a batch file. Below is a sample script to do so. @ echo off REM Sample Script to look for a process and kill another process if earlier process is not running REM Error level 1