Archive for the ‘Programming’ Category

How to make for loop (cycles) in KSH useful for FreeBSD / UNIX system administrators

Friday, November 3rd, 2017

korn-shell-how-to-make-loops-easily-for-sys-admin-purposes

Sometimes we have to administrate this operating systems such as FreeBSD / AIX / HP UX or even Mac OS server where by default due to historical reasons or for security bash shell is not avialable. That's not a common scenario but it happens so if as sysadmin we need to create for loops on ksh it is useful to know how to do that, as for loop cycles are one of the most important command line tools the sysadmin swiss army knife kind of.

So how to create a for loop (cycle) in ksh (Korn Shell)?

The most basic example for a KSH loop shell is below:
 

#!/bin/ksh
for i in 1 2 3 4 5
do
  echo "Welcome $i times"
done

 


Add the content to any file lets say ksh_loop.ksh then make it executable as you do in bash shells

 

 

$ chmod +x ksh_loop.ksh
$ ksh ksh_loop.ksh

 


The overall syntax of the for loop ksh command is as follows:

 

 

for {Variable} in {lists}
do
    echo ${Variable}
done

 


Hence to list lets say 20 iterations in a loop in ksh you can use something like:
 

#!/bin/ksh
for i in {1..20}
do
  echo "Just a simple echo Command $i times";
# add whatever system commands you like here
done

 


Example for some useful example with KSH loop is to list a directory content so you can execute whatever command you need on each of the files or directories inside

 

#!/bin/ksh
for f in $(ls /tmp/*)
do
        print "Iterating whatever command you like on /tmp dir : $f"
done


Other useful for loop iteration would be to print a file content line by line just like it is done in bash shell, you can do that with a small loop like belows:

 

#!/bin/ksh
for iteration_variable in $(cat  file_with-your-loved-content-to-iterate.txt)
do
        print "Current iteration like is : $iteration_variable"
done

 

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Command to get CPU server load in % percentage using bash and /proc/stat on Linux

Wednesday, March 11th, 2015

Command-to-get-CPU-server-load-in-percentage-using-bash-shell-script-and-linux-proc-stat

Getting load avarage is easy with uptime command, however since nowadays Linux servers are running on multiple CPU machines and Dual cores, returned load avarage shows only information concerning a single processor. Of course seeing overall CPU server load is possible with TOP / TLoad command  / HTOP and a bunch of other monitoring commands, but how you can get a CPU percentage server load using just  /proc/stat and bash scripting? Here is hwo:
 

:;sleep=1;CPU=(`cat /proc/stat | head -n 1`);PREV_TOTAL=0;for VALUE in "${CPU[@]}”; do let “PREV_TOTAL=$PREV_TOTAL+$VALUE”;done;PREV_IDLE=${CPU[4]};sleep $sleep; CPU=(`cat /proc/stat | head -n 1`);unset CPU[0];IDLE=${CPU[4]};TOTAL=0; for VALUE in “${CPU[@]}"; do let "TOTAL=$TOTAL+$VALUE"; done;echo $(echo "scale=2; ((($sleep*1000)*(($TOTAL-$PREV_TOTAL)-($IDLE-$PREV_IDLE))/($TOTAL-$PREV_TOTAL))/10)" | bc -l );

52.45

As you can see command output shows CPU is loaded on 52.45%, so this server will soon have to be replaced with better hardware, because it gets CPU loaded over 50%

It is useful to use above bash shell command one liner together with little for loop to refresh output every few seconds and see how the CPU is loaded in percentage over time.

 

for i in $(seq 0 10); do :;sleep=1;CPU=(`cat /proc/stat | head -n 1`);PREV_TOTAL=0;for VALUE in "${CPU[@]}”; do let “PREV_TOTAL=$PREV_TOTAL+$VALUE”;done;PREV_IDLE=${CPU[4]};sleep $sleep; CPU=(`cat /proc/stat | head -n 1`);unset CPU[0];IDLE=${CPU[4]};TOTAL=0; for VALUE in “${CPU[@]}"; do let "TOTAL=$TOTAL+$VALUE"; done;echo $(echo "scale=2; ((($sleep*1000)*(($TOTAL-$PREV_TOTAL)-($IDLE-$PREV_IDLE))/($TOTAL-$PREV_TOTAL))/10)" | bc -l ); done

47.50

13.86
27.36
82.67
77.18

To monitor "forever" output from all server processor overall load use:
 

while [ 1 ]; do :;sleep=1;CPU=(`cat /proc/stat | head -n 1`);PREV_TOTAL=0;for VALUE in “${CPU[@]}”; do let “PREV_TOTAL=$PREV_TOTAL+$VALUE”;done;PREV_IDLE=${CPU[4]};sleep $sleep; CPU=(`cat /proc/stat | head -n 1`);unset CPU[0];IDLE=${CPU[4]};TOTAL=0; for VALUE in “${CPU[@]}"; do let "TOTAL=$TOTAL+$VALUE"; done;echo $(echo "scale=2; ((($sleep*1000)*(($TOTAL-$PREV_TOTAL)-($IDLE-$PREV_IDLE))/($TOTAL-$PREV_TOTAL))/10)" | bc -l ); done

 

 

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How to check Apache Webserver and MySQL server uptime – Check uptime of a running daemon with PS (process) command

Tuesday, March 10th, 2015

check_Apache_Webserver_and_MySQL_server_uptime_-_Check-uptime-of-running-daemon-service-with-PS-process-command

Something very useful that most Apache LAMP (Linux Apache MySQL PHP) admins should know is how to check Apache Webserver uptime and MySQL server running (uptime).
Checking Apache / MySQL uptime is primary useful for scripting purposes – creating auto Apache / MySQL service restart scripts, or just as a quick console way to check what is the status and uptime of Webserver / SQL.

My experience as a sysadmin shows that lack of Periodic Apache and MySQL restart every week or every month often creates sys-admin a lot of a headaches cause (Apache / NGINX / SQL  server) starts eating too much memory or under some circumstances leads to service or system crashes. Periodic system main services restart is especially helpful in case if Website's backend programming code is writetn in a bad and buggy uneffient way by unprofessional (novice) programmers.
While I was still working as Senior SysAdmin in Design.BG, I've encountered many such Crappy Web applications developed by dozen of different programmers (because company's programmers changed too frequently and many of the hired Web Developers ,were still learning to program, I guess same is true also for other Start-UP Web / IT Company where crappy programming code is developed you will certainly need to keep an eye on Apache / MYSQL uptime.  If that's the case below 2 quick one liners with PS command will help you keep an eye on Apache / MYSQL uptime

 

ps -eo "%U %c %t"| grep apache2 | grep -v grep|grep root
root     apache2            02:30:05

Note that above example is Debian specific on RPM based distributions you will have to grep for httpd instead of apache2
 

ps -eo "%U %c %t"| grep http| grep -v grep|grep root

root     apache2            10:30:05

To check MySQL uptine:
 

ps -eo "%U %c %t"| grep mysqld
root     mysqld_safe        20:42:53
mysql    mysqld             20:42:53


Though example is for mysql and Apache you can easily use ps cmd in same way to check any other Linux service uptime such as Java / Qmail / PostgreSQL / Postfix etc.
 

ps -eo "%U %c %t"|grep qmail
qmails   qmail-send      19-01:10:48
qmaill   multilog        19-01:10:48
qmaill   multilog        19-01:10:48
qmaill   multilog        19-01:10:48
root     qmail-lspawn    19-01:10:48
qmailr   qmail-rspawn    19-01:10:48
qmailq   qmail-clean     19-01:10:48
qmails   qmail-todo      19-01:10:48
qmailq   qmail-clean     19-01:10:48
qmaill   multilog        40-18:02:53

 

 ps -eo "%U %c %t"|grep -i nginx|grep -v root|uniq
nobody   nginx           55-01:22:44

 

ps -eo "%U %c %t"|grep -i java|grep -v root |uniq
hipo   java            27-22:02:07

 

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How to SSH client Login to server with password provided from command line as a script argument – Running same commands to many Linux servers

Friday, March 6th, 2015

ssh-how-to-login-with-password-provided-from-command-line-use-sshpass-to-run-same-command-to-forest-of-linux-servers

Usually admins like me who casuanlly need to administer "forests" (thousands of identicallyconfigured services Linux servers) are generating and using RSA / DSA key authentication for passwordless login, however this is not always possible as some client environments does prohibit the use of RSA / DSA non-pass authentication, thus in such environments to make routine server basic package rpm / deb upgrades or do other maintanance patching its necessery to use normal ssh user / pass login but as ssh client doesn't allow password to be provided from prompt for security reasons and therefore using some custom bash loop to issue single command to many servers (such as explained in my previous article) requires you to copy / paste password on password prompt multiple times. This works its pretty annoying so if you want to run single command on all your 500 servers with specifying the password from password prompt use sshpass tool (for non-interactive ssh password auth).

SSHPASS official site description:
 

sshpass is a utility designed for running ssh using the mode referred to as "keyboard-interactive" password authentication, but in non-interactive mode.

 

Install sshpass on Debian / Ubuntu (deb based) Linux

sshpass is installable right out of regular repositories so to install run:
 

apt-get install —yes sshpass


Install sshpass on CentOS / Fedora (RPM based) Linux


sshpass is available also across most RPM based distros too so just use yum package manager

 

yum -y install sshpass


If its not available across standard RPM distro provided repositories, there should be RPM on the net for distro just download latest one and use wget and rpm to install:

 wget -q http://dl.fedoraproject.org/pub/epel/6/x86_64/sshpass-1.05-1.el6.x86_64.rpm

 rpm -ivh sshpass-1.05-1.el6.x86_64.rpm

 

How Does SshPass Works?

 

Normally openssh (ssh) client binary uses direct TTY (/dev/tty)= an abbreviation for PhyTeleTYpewriter or (the admin jargon call Physical Console access)  instead of standard remotely defined /dev/ptsVirtual PTY.
To get around this Sshpass runs ssh in a dedicated TTY to emulate the password is indeed issues by interactive keyboard user thus  fooling remote sshd server to thinking password
is provided by interactive user.


SSHPass use

Very basic standard use which allows you to pass the password from command line is like this:
 

sshpass -p 'Your_Password_Goes_here123' ssh username@server.your-server.com


Note that the server you're working is shared with other developers they might be able to steal your username / password by using a simple process list command such as:
 

 ps auxwwef


In my case security is not a hot issue, as I'm the only user on the server (and only concern might be if someone hacks into the server 🙂 

 

Then assuming that you have a plain text file with all your administered servers, you can easily use sshpass in a Bash Script loop in order to run, lets say a package upgrade across all identical Linux version machines:
 

while read line; do
sshpass -p 'Your_Password_Goes_here123' ssh username@$line "apt-get update && apt-get upgrade && apt-get dist-upgrade" < /dev/null;
done < all_servers_list.txt

Change the command you like to issue across all machines with the string "apt-get …"
Above command can be used to keep up2date all Debian stable server packages. What you will do on servers is up to your imaginations, very common use of above line would be if you want to see uptime /netstat command output across all your network servers.

 

while read line; do
sshpass -p 'Your_Password_Goes_here123' ssh username@$line "uptime; who; netstat -tunlp; " < /dev/null;
done < all_servers_list.txt

 


As you can guess SshPass is swiss army knife tool for admins whoneed to automate things with scripts simultaneously across number of servers.
 

Happy SSH-ing 🙂

 

 

 

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Remove \r (Carriage Return) from string with standard bash shell / sed / tr / vim or awk – Replace \r hidden messy characters from files

Tuesday, February 10th, 2015

remove_r_carriage_return_from_string_with-standard-bash_shell_sed_tr_or_awk_replace_annoying_hidden_messy_characters_from_files

I've been recently writting this Apache webserver / Tomcat / JBoss / Java decomissioning bash script. Part of the script includes extraction from httpd.conf of DocumentRoot variable configured for Apache host.
I was using following one liner to grep and store DocumentRoot set directory into new variable:

documentroot=$(grep -i documentroot /usr/local/apache/conf/httpd.conf | awk '{ print $2 }' |sed -e 's#"##g');

Above line greps for documentroot prints 2nd column of the matchi (which is the Apache server set docroot and then removes any " chars).

However I faced the issue that parsed string contained in $documentroot variable there was mysteriously containing r – return carriage – this is usually Carriage Return (CR) sent by Mac OS and Apple computers. For those who don't know the End of Line of files in UNIX / Linux OS-es is LF – often abreviated as n – often translated as return new line), while Windows PCs use for EOF CR + LF – known as the infamous  rn. I was running the script from the server which is running SuSE SLES 11 Linux, meaning the CR + LF end of file is standardly used, however it seem someone has editted the httpd.conf earlier with a text editor from Mac OS X (Terminal). Thus I needed a way to remove the r from CR character out of the variable, because otherwise I couldn't use it to properly exec tar to archive the documentroot set directory, cause the documentroot directory was showing unexistent.

Opening the httpd.conf in standard editor didn't show the r at the end of
"directory", e.g. I could see in the file when opened with vim

DocumentRoot "/usr/local/apache/htdocs/site/www"

However obviously the r character was there to visualize it I had to use cat command -v option (–show-nonprinting):

cat -v /usr/local/apache/conf/httpd.conf

DocumentRoot "/usr/local/apache/htdocs/site/wwwr"


1. Remove the r CR with bash

To solve that with bash, I had to use another quick bash parsing that scans through $directory and removes r, here is how:

documentroot=${documentroot%$'r'}

It is also possible to use same example to remove "broken" Windows rn Carriage Returns after file is migrated from Windows to Liunx /  FreeBSD host:

documentroot=${documentroot%$'rn'}

 

2. Remove r Carriage Return character with sed

Other way to do remove (del) Windows / Mac OS Carriage Returns in case if Migrating to UNIX is with sed (stream editor).

sed -i s/r// filename >> filename_out.txt


3. Remove r CR character with tr

There is a third way also to do it with (tr) – translate or delete characters old shool *nix command:

tr -d 'r' < file_with_carriagereturns > file_without_carriage_returns

 

4. Remove r CRs with awk (pattern scanning and processing language)

 awk 'sub("$", "r")' inputf_with_crs.txt > outputf_without_crs.txt


5. Delete r CR with VIM editor

:%s/r//g


6. Converting  file DOS / UNIX OSes with dos2unix and unix2dos command line tools

For sysadmins who don't want to bother with writting code to convert CR when moving files between Windows and UNIX hosts there are dos2unix and unix2dos installable commands.

All done Cheers ! 🙂

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Speed up Apache webserver by including htaccess mod_rewrite rules in VirtualHosts / httpd.conf

Wednesday, November 12th, 2014

speed-up-apache-through-include-htaccess-from-config
There are plenty of Apache Performance Optimization things to do on a new server. However many sysadmins miss  .htaccess mod_rewrite rules whole optimization often leads to a dramatic performance benefits and low webserver responce time, making website much more attractive for both Search Engine Crawlers and End User experience.

Normally most Apache + PHP CMS systems, websites, blogs etc. are configured to use various goodies of .htaccess files (mostly mod_rewrite rules, directory htpasswd authentication  and allow forbid directives). All most popular open-source Content management systems  like Drupal, Joomla, WordPress, TYPO3, Symphony CMS are configured to get use  .htaccess file usually living in the DocumentRoot of a virtualhost ( website/s )httpd.conf , apache2.conf /etc/apache2/sites-enabled/customvhost.com or whichever config the Vhost resides…

It is also not uncommon practice to enable .htaccess files to make programmers life easier (allowing the coder to add and remove URL rewrite rules that makes URL pretty and SEO friendly, handle website redirection or gives live to the framework like it is the case with Zend PHP Framework).

However though having the possibility to get the advantages of dynamically using .htaccess inside site DocRoot or site's subdirectories is great for developers it is not a very good idea to have the .htaccess turned on Production server environment.

Having

AllowOverride All

switched on for a directory in order to have .htaccess enabled, makes the webserver lookup for .htaccess file and re-read its content dynamically on each client request.
This has a negative influence on overall server performance and makes Apache preforked childs or workers (in case of mpm-worker engine used) to waste time parsing .htaccess file leading to slower request processing.

Normally a Virtualhost with enabled .htaccess looks like so:

<VirtualHost 192.168.0.5:80>
ServerName your-website.com:80 …
DocumentRoot /var/www/website
<Directory /var/www/website>
AllowOverride All …
</Directory> …
</VirtualHost>

And VirtualHost configured to keep permanently loaded mod_rewrite .htaccess rules in memory on Apache server start-up.
 

<VirtualHost 192.168.0.5:80>
ServerName your-website.com:80 …
DocumentRoot /var/www/website
<Directory /var/www/website>
AllowOverride None
Include /var/www/website/.htaccess …
</Directory> …
</VirtualHost>

Now CMS uses the previous .htaccess rules just as before, however to put more rewrite rules into the file you will need to restart webserver which is a downside of using rewrite rules through the Include directive. Using the Include directive instead of AllowOverride leads to 7 to 10% faster individual page loads.

I have to mention Include directive though faster has a security downside because .htaccess files loaded with Include option (uses mod_include) via httpd.conf doesn't recognize <Directory> … </Directory> set security rules. Also including .htaccess from configuration on Main Website directory, could make any other sub-directories .htaccess Deny / Allow access rules invalid and this could expose site to  security risk. Another security downside is because Include variable allows loading a full subset of Apache directives (including) loading other Apache configuration files (for example you can even override Virtualsthost pre-set directives such as ErrorLog, ScriptAlias etc.) and not only .htaccess standard directives allowed by AllowOverride All. This gives a potential website attacker who gains write permissions over the included /var/www/website/.htaccess access to this full set of VirtualHost directives and not only .htaccess standard allowed.

Because of the increased security risk most people recommend not to use Include .htaccess rules, however for those who want to get the few percentage page load acceleration of using static Include from Apache config, just set your Included .htaccess file to be owned by user/group root, e.g.:

chown root:root /var/www/website/.htaccess

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Linux find files while excluding / ignoring some files – Show all files on UNIX excluding hidden . (dot) files

Friday, August 22nd, 2014

linux-find-files-while-excluding-ignoring-some-files-show-all-files-on-unix-excluding-hidden-dot-files
A colleague of mine (Vasil) asked me today, how he can recursively chmod to all files in a directory while exclude unreadable files for chmod (returning permission denied). He was supposed to fix a small script which was supposed to change permissions like :

chmod 777 ./
chmod: cannot access `./directory': Permission denied
chmod: cannot access `./directory/file': Permission denied
chmod: cannot access `./directory/onenote': Permission denied

First thing that came to my mind was to loop over it with for loop and grep out only /directory/ and files returning permissioned denied.

for i in $(find . -print | grep -v 'permission denied'); do echo chmod 777 $i; done

This works but if chmod has to be done to few million of files, this could be a real resource / cpu eater.

The better way to do it is by only using Linux find command native syntax to omit files.

find . -type f ( -iname "*" ! -iname "onenote" ! -iname "file" )

Above find will print all files in . – current directory from where find is started, except files: onenote and file.
To exclude
 

Search and show all files in Linux / UNIX except hidden . (dot) files

Another thing he wanted to do is ignore printing of hidden . (dot) files like .bashrc, .profile and .bash_history while searching for files – there are plenty of annoying .* files.

To ignore printing with find all filesystem hidden files from directory:

find . -type f ( -iname "*" ! -iname ".*" )

on web hosting webservers most common files which is required to be omitted on file searches is .htaccess

find . -type f ( -iname "*" ! -iname ".htaccess" )

  In order to print only all hidden files in directory except .bashrc and .bash_profile:

find . -type f ( -iname '.*' ! -iname '.bashrc' ! -iname '.bash_profile' )

Another useful Linux find use for scripting purposes is listing only all files presented in current directory (simulating ls), in case if you wonder why on earth to use find and not a regular ls command?, this is useful for scripts which has to walk through millions of files (for reference see how to delete million of files in same folder with Linux find):

find . ! -name . -prune

./packages
./bin
./package

"! -name . " –  means any file other than current directory

prune – prunes all the directories other than the current directory.

A more readable way to list only files in current folder with find is – identical to what above cmd:

find ./* -prune

./packages
./bin
./mnt

If you want to exclude /mnt folder and its sub-directories and files with find by using prune option:

find . -name tmp -prune -o -print

 

 

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