LUN Scaning Script for RHEL 5.X

Step 1 : Run the below script to scan the LUN,

#!/bin/bash
#
# Lun Scanning script
# Works on RHEL 5.X
#
for i in `ls /sys/class/fc_host`
do
echo "1" > /sys/class/fc_host/$i/issue_lip
echo "- - -" > /sys/class/scsi_host/$i/scan
done

Step 2 : Check Lun Visibility in Server

# fdisk -l

INODE Explained

INODE – Index Node (Also called as Index Number) is the basic and fundamental concept in Linux filesystem.

Each file in Linux has following attributes,

• File type (executable, block special or character special etc)
• Permissions (read, write, execute)
• Owner
• Group
• File Size
• File access, change and modification time
• File deletion time
• Number of links (soft/hard)
• Extended attribute (Like no one can delete/append only..)
• Access Control List (ACLs)

All the above information is stored in inode & every file has unique inode value in filesystem which identifies the file attributes.

We can get the inode value by ls & stat command

Note :

Remember that Linux never stores the file creation time.

How to Create and Install an Apache Self Signed Certificate

Below steps is for creating and installing apache self signed certificate in RHEL 6.2

Step 1 : Generate Key

[root@mail ]# cd /etc/ssl/certs/
[root@mail certs]# openssl genrsa -des3 -out new.key 2048
Generating RSA private key, 2048 bit long modulus
.........................................................................................................+++
...............................................................................................................+++
e is 65537 (0x10001)
Enter pass phrase for new.key:
Verifying - Enter pass phrase for new.key:
[root@mail certs]#


Step 2 : Removing passphrase from key (This step is optional, by this step we can avoid giving password every time we start apache service - httpd)

[root@mail certs]# cp new.key new.key_org
[root@mail certs]#
[root@mail certs]# openssl rsa -in new.key -out new.key
Enter pass phrase for new.key:
writing RSA key
[root@mail certs]# ll new.key
-rw-r--r-- 1 root root 1679 May 22 12:13 new.key
[root@mail certs]#

Step 3 : Generate a Certificate Signing Request (CSR)

[root@mail certs]# openssl req -new -key new.key -out webmail.csr
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [XX]:IN
State or Province Name (full name) []:Tamil Nadu
Locality Name (eg, city) [Default City]:Madurai
Organization Name (eg, company) [Default Company Ltd]:Lynx Corp
Organizational Unit Name (eg, section) []:Leo
Common Name (eg, your name or your server's hostname) []:mail.isvivek.com
Email Address []:isvivek@isvivek.com

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
[root@mail certs]#


Step 4 :  Generate a self signed ssl certificate

[root@mail certs]# openssl x509 -req -days 365 -in webmail.csr -signkey new.key -out webmail.cert
Signature ok
subject=/C=IN/ST=Tamil Nadu/L=Madurai/O=Lynx Corp/OU=Leo/CN=mail.isvivek.com/emailAddress=isvivek@isvivek.com
Getting Private key
[root@mail certs]#


Step 5 : Installing generated ceritificate

[root@mail certs]# vim /etc/httpd/conf.d/ssl.conf

--->>Update it as follows

SSLRandomSeed startup file:/dev/urandom 1024
SSLRandomSeed connect file:/dev/urandom 1024

--->> Update VirtualHost as follows:


    SSLEngine On
    SSLCertificateFile /etc/ssl/certs/webmail/webmail.cert
    SSLCertificateKeyFile /etc/ssl/certs/webmail/new.key
    SSLProtocol All -SSLv2
    SSLCipherSuite HIGH:MEDIUM:!aNULL:+MD5
    DocumentRoot "/var/www/html/ssl"
    ServerName mail.isvivek.com:443

[root@mail certs]#  mkdir -p /var/www/html/ssl
[root@mail certs]#  chown apache /var/www/html/ssl

[root@mail certs]# vim /etc/httpd/conf/httpd.conf

--->>Update it as follows


         SSLRequireSSL
         SSLOptions +StrictRequire
         SSLRequire %{HTTP_HOST} eq "mail.isvivek.com"
         ErrorDocument 403 https://mail.isvivek.com/sslerror.html



[root@mail certs]# /etc/init.d/httpd restart
Stopping httpd:                                            [  OK  ]
Starting httpd:                                             [  OK  ]
[root@mail certs]#

Step 6 :  Verify the details from by browsing the URL,

Pseudo Terminals Limits

"/proc/sys/kernel/pty/max" file defines the maximum number of pseudoterminals,

[root@mail ~]# cat /proc/sys/kernel/pty/max

4096

[root@mail ~]#


"/proc/sys/kernel/pty/nr" is read-only file indicates how many pseudoterminals are currently in use

[root@mail ~]# cat /proc/sys/kernel/pty/nr

4

[root@mail ~]#

To limit or increase the Pseudo Terminals Permanently, 

# vim /etc/sysctl.conf

kernel.pty.max = 1024

#  sysctl -p

After the pty limits you will get below error if you try to open new session,