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This shows you the differences between two versions of the page.

--- how_to [2016/07/19 20:54] – k2patel
+++ how_to [2020/08/10 02:35] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
+====== How to ..... ======
+==== .gvfs ====
+How to get rid of .gvfs and what it is.
+What it is
+GVFS is a replacement for GnomeVFS, the GNOME Virtual File System
+{User_home}/.gvfs is used as a mount point for the Gnome gvfs for user.
+It stays mounted even when user is logged off.You need to umount  it prior to delete it.
+Use following command to unmount
+<code bash>
+umount -fl /home/xyz/.gvfs
+</code>
+==== How to drop all table from database (mysql) ====
+To drop all the table in the mysql database - use the following command.
+<WRAP prewrap>
+<code mysql>
+mysqldump -u[USERNAME] -p[PASSWORD] --add-drop-table --no-data [DATABASE] | grep ^DROP | mysql -u[USERNAME] -p[PASSWORD] [DATABASE]
+</code>
+</WRAP>
+==== How to list pear using php ====
+First install PEAR_Info
+<code bash>
+pear install PEAR_Info
+</code>
+Than create file pearinfo.php with following content.
+<code php>
+<?php
+require_once 'PEAR/Info.php';
+$info = new PEAR_Info();
+$info->display();
+?>
+</code>
+Now browse the file in your favorite browser.
+==== How to list Installed CPAN Modules ====
+<code perl>
+#!/usr/bin/perl
+use ExtUtils::Installed;
+my $instmod = ExtUtils::Installed->new();
+foreach my $module ($instmod->modules()) {
+my $version = $instmod->version($module) || "???";
+       print "$module -- $version\n";
+}
+</code>
+==== Watch output of command with refresh ====
+This can me usefull to monitor command with no refresh. like vmstat, iostat
+<code bash>
+watch -n 3 vmstat -D
+</code>
+==== Force Change password next login ====
+<code bash>
+chage -d 0 <Username>
+</code>
+==== Setting up Multiple ip using single file ====
+You can add IP range to server using following way.
+Range file :\\
+replace "eth0" with your nic name in file name.\\
+CLONENUM_START - change based on range you add to NIC.\\
+in respect of below configuration next CLONENUM_START for eth0 is "6"\\
+<code bash | /etc/sysconfig/network-scripts/ifcfg-eth0-range0>
+IPADDR_START=192.168.1.25
+IPADDR_END=192.168.1.30
+CLONENUM_START=0
+</code>
+==== Setting up Multiple Block of IP to single NIC/server ====
+In normal case if you add diff. block of IP only one block will work.\\
+As gateway for all block might be different.\\
+In that case you need to add following line to config.\\
+<code bash | /etc/sysconfig/network >
+GATEWAYDEV="eth0"
+</code>
+NOTE : replace eth0 based on your NIC name
+==== Getting Old Version of PHP package from cvs ====
+From : [[http://php.net]]
+Setting up cvs client. (Recommended)
+<code bash | ~/.cvsrc>
+cvs -z3
+update -d -P
+checkout -P
+diff -u
+</code>
+Login to cvs server using anonymous login\\
+**password : phpfi**
+<code bash>
+cvs -d :pserver:cvsread@cvs.php.net:/repository login
+</code>
+Download source from cvs.\\
+Make sure you replace php_5_2_5 with your version need (e.g. php_4_0_3)
+<code bash>
+cvs -d :pserver:cvsread@cvs.php.net:/repository checkout -r php_5_2_5 php-src
+</code>
+Now you have clean version of sources on your machine.\\
+In order to generate configure script you need to run following.
+<code bash>
+./buildconf
+</code>
+To build package use following.\\
+Replace versions with your checkout snap.\\
+**makedist <package> <version>**
+<code bash>
+sh makedist php 5.2.5
+</code>
+//
+You just make your own distribution package.//
+==== How to test UDP Connection ====
+This is needed in many cases. Many services still use UDP port for Authentication / Certification for software.\\
+You can test connection using nmap.
+<code bash>
+# nmap -p [port] -sU -P0 [host name | ip address]
+# nmap -p 234 -sU -P0 xx.xx.xx.xx
+# nmap -p 543 -sU -P0 xx.xx.xx.xx
+</code>
+Also you can use netcat
+<code bash>
+nc -zu <ip> <udpport>
+</code>
+==== ip_conntrack: table full, dropping packet ====
+I found myself with a server under normal load.\\
+but, it no network connections initiated. and log is full of entry as below
+<code bash>
+ip_conntrack: table full, dropping packet
+</code>
+After searching on google found [[http://kbase.redhat.com/faq/FAQ_45_11238.shtm | Redhat]] site for more details. \\
+It seems server was running iptables, but it was under a very heavy load and also handling a high volume of network connections.\\
+Generally, the ip_conntrack_max is set to the total MB of RAM installed multiplied by 16.\\
+However, this server had 2GB of RAM, but ip_conntrack_max was set to 65536:
+<code bash>
+# cat /proc/sys/net/ipv4/ip_conntrack_max
+</code>
+I have checked with few other server and all had ip_conntrack_max set to 65536.\\
+I’m not sure seems default value to me.
+Now i have found my value using following:
+<code bash>
+# cat /proc/sys/net/ipv4/netfilter/ip_conntrack_count
+</code>
+and i have adjusted using following. about 8GB ram.
+<code bash>
+# echo 131072 > /proc/sys/net/ipv4/ip_conntrack_max
+</code>
+But, above change is temporary to set value at boot do following.
+<code bash | /etc/sysctl.conf>
+net.ipv4.ip_conntrack_max=131072
+</code>
+This should be it.
+==== Crontab with own php.ini and send result to mail ====
+If you need to run cron with your own php.ini and send result to mail use following.
+<WRAP prewrap>
+<code bash>
+*/1 */2 * * * /usr/local/bin/php --php-ini /srv/www/conf/php.ini /srv/www/public_html/cron.php | /usr/bin/mail -s "Output of crontab" xyz@yahoo.com
+</code>
+</WRAP>
+==== Exit Codes ====
+At some point you feel like there is no exit code documentation and you want find you what should it return.\\
+There is simple practical way to find exit code in linux.\\
+<code bash>
+echo $?
+</code>
+which determine what exit code was returned by a command. must be post run this after command.\\
+following is simple example.\\
+<code bash>
+ls bcd
+ls: bcd: No such file or directory
+echo $?
+</code>
+Which as ls return "2" serious trouble. file not found.\\
+If 0 All OK.\\
+You can post run with any command and find out what is the return code. This will help you as quick fix.\\
+In logical programming you must have all the exit codes for best result.
+==== How to use serial console ====
+Here is the simple how to on using serial console.
+First find out how many serial device is connected.
+<code bash>
+dmesg | grep tty
+</code>
+Which should return following results.
+<code text>
+serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
+serial8250: ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A
+:0a: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
+:0b: ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A
+</code>
+On my machine it find only two ports.\\
+so i am using "[01]" for those two ports. if you have more add number like "[012..]".\\
+Now Initialize those ports.\\
+<code bash>
+setserial -g /dev/ttyS[01]
+</code>
+You are all set.\\
+Now connect to serial port using minicom.\\
+<code bash>
+minicom -o
+</code>
+This works for me.
+==== How to grab External IP ====
+I needed clean and most frequent access to find outgoing IP of servers.\\
+So based on Environment variable i have developed small script. [[cgi_script_to_print_visitor_ip|script to grab visitor IP]] \\
+which print your external IP.\\
+<code bash>
+curl ip.k2patel.in
+</code>
+NOTE :
+  * I do not track or log any request coming to above domain.
+  * But in case of any excessive amount of request i might enable logging to block such activity.
+==== Truncate on Linux ====
+Not sure what make truncate command to disappear from linux.\\
+But it is/was really usefull tool. following is alternative way to reduce file size.\\
+Command below will reduce size to 100MB, and it takes argument in bytes. replace according to your need. (replace bs="")
+<code bash>
+dd if=/dev/null of=msyql_slow.txt seek=1 bs=104857600
+</code>
+==== Removing Patch ====
+To remove applied patch use following command.
+<code bash>
+patch -R
+</code>
+==== Preserve Custom nameserver ====
+To preserve custom nameserver while using DHCP you need to modify config file.\\
+add or update following line.
+<code bash | /etc/dhcp/dhclient.conf>
+prepend domain-name-servers 4.2.2.1,8.8.8.8;
+</code>
+Redhat / Fedora
+NM looks for /etc/dhclient-<interface>.conf then /etc/dhcp/dhclient-<interface>.conf \\
+and will merge the first found into the dhclient config files it produces.
+==== Enable port below 1024 for all users ====
+NOTE : Please be aware it is not / never advisable.
+Now if you want java to use port below 1024 you can use following command.
+<code bash>
+setcap 'cap_net_bind_service=+ep' /usr/bin/java
+</code>
+NOTE : It is only available on RHEL6/CentOS6 and up
+==== Building Software RAID ====
+One of nice feature about software RAID is you can get good performance using it.\\
+Here is the simple steps to follow to create software raid level 10.
+**Step 1** : Create Partition Assign //type - fd//
+<code bash>
+fdisk /dev/sdf
+fdisk /dev/sdg
+fdisk /dev/sdh
+fdisk /dev/sdi
+</code>
+**Step 2** : Create Raid Drive. ( this command will create "/dev/md10" )
+<WRAP prewrap>
+<code bash>
+mdadm --create --level=10 --raid-devices=4 --spare-devices=0 --chunk=128 --layout=f2 /dev/md10 /dev/sdf1 /dev/sdg1 /dev/sdh1 /dev/sdi1
+</code>
+</WRAP>
+**Step 3**: Format Drive ( I am formatting for XFS )
+<code bash>
+mkfs.xfs /dev/md10
+</code>
+** Moving Between Machine **
+create if you don't have it already
+<note warning>
+Do not keep or include UUID in destination System, Simply copy rest of the part leaving UUID behind.
+</note>
+Source System :
+<code bash>
+mdadm --examine --scan > /etc/mdadm.conf
+mdadm --stop /dev/md10
+</code>
+Destination System :\\
+Add / Create mdadm
+<code bash | /etc/mdadm.conf>
+ARRAY /dev/md10 level=raid10 num-devices=4 metadata=0.90 devices=/dev/sdg1,/dev/sdh1,/dev/sdi1,/dev/sdj1
+</code>
+Now assemble it on new system.
+<code bash >
+mdadm --assemble --scan --verbose /dev/md10 /dev/sdg1 /dev/sdh1 /dev/sdi1 /dev/sdj1
+</code>
+Mount /dev/md10 - Enjoy.!!
+==== ramfs on Linux ====
+<note warning>Do not confuse your self with tmpfs and ramfs as both are diff. entity</note>
+To create/mount ramfs you can use following command.\\
+Please make sure folder already exists.
+<code bash>
+mount -t ramfs none /tmp/toall
+</code>
+==== Reduce default tmpfs size ====
+Default size of **/dev/shm** is almost 50% of your memory.\\
+In order to reduce it to some optimal value you can update your /etc/fstab.\\
+just add size variable in your option field : comma saperated : will do.
+<code bash>
+tmpfs                   /dev/shm                tmpfs   defaults,size=8g        0 0
+</code>
+==== Password Hashing Algorithm ====
+=== Display Hashing Algorithm on server ===
+<code bash>
+authconfig --test | grep hashing
+</code>
+=== Change Algorithm on server ===
+<code bash>
+authconfig --passalgo=sha512 --update
+</code>
+==== Changing encrypted file system password ====
+If you have encrypted partitions you can change password using following commands.
+<note warning>Replace sda2 with your drive number</note>
+=== Check which key slot is occupied ===
+<code bash>
+cryptsetup luksDump /dev/sda2
+</code>
+=== Now add key to next free slot ===
+<code bash>
+cryptsetup luksAddKey /dev/sda2
+</code>
+=== Now remove / Disable Previous slot ===
+<code bash>
+cryptsetup luksKillSlot /dev/sda2 0
+</code>
+==== Check for Operation Windigo infection ====
+<code bash>
+ssh -G 2>&1 | grep -e illegal -e unknown > /dev/null && echo “System clean” || echo “System infected”
+</code>
+[[http://news.softpedia.com/news/quot-Operation-Windigo-quot-Attack-Infects-10-000-Unix-Servers-Millions-of-PCs-at-Risk-432920.shtml?utm_source=dlvr.it&utm_medium=twitter|Ref.]]
+==== Creating patch for rpm ====
+this can be used as '%patch0 -p1 -b <file_name>'
+<code bash>
+diff -ru hdf-4.2.12-orig hdf-4.2.12-diff >| ../SOURCES/hdf-4.2.12.example.patch
+</code>
+==== Configure option for Fedora / Redhat ====
+replace amaya with your application etc...\\
+This is usefull while compiling sources for systems
+<WRAP prewrap>
+<code bash>
+../configure -enable-system-raptor '--build=x86_64-redhat-linux-gnu' '--host=x86_64-redhat-linux-gnu' '--program-prefix=' '--prefix=/usr' '--exec-prefix=/usr' '--bindir=/usr/bin' '--sbindir=/usr/sbin' '--sysconfdir=/etc' '--datadir=/usr/share' '--includedir=/usr/include' '--libdir=/usr/lib64' '--libexecdir=/usr/libexec' '--sharedstatedir=/var/lib' '--mandir=/usr/share/man' '--infodir=/usr/share/info' '--exec_prefix=/usr' 'build_alias=x86_64-redhat-linux-gnu' 'host_alias=x86_64-redhat-linux-gnu' '--libexecdir=/usr/lib64/amaya' '--localstatedir=/var' '--datadir=/usr/share/amaya' '--sysconfdir=/etc/amaya' '--with-logdir=$(localstatedir)/log/amaya' '--with-pidfile=$(localstatedir)/run/amaya.pid'
+</code>
+</WRAP>
+==== Run single command parallel'y with diff values ====
+<WRAP prewrap>
+<code bash>
+(echo "http://test.k2patel.in"; echo "http://test.ornl.gov"; echo "http://yahoo.com" ) | parallel 'ab -n 50 -c 50 {}'
+</code>
+</WRAP>
+==== Print yum variable value ====
+<code python>
+import yum
+import pprint
+yvar = yum.YumBase()
+pprint.pprint(yvar.conf.yumvar, width=1)
+</code>
+==== Disable Predictable interface name in RHEL / CentOS ====
+Pass following during boot kernel command line.
+<code bash>
+net.ifnames=0
+</code>