How to scan newly added LUN using rescan-scsi-bus.sh ?

ENV : RHEL 5.4 and later

I suggest you NOT to scan the existing LUNs since I/O operations are still in use and if you scan them it will/may corrupt the file system. So, I always suggest you to scan the new added device or storage. Once you add it, HBA will detect the device and then you can scan this non-existent LUNs to the HBA. As an example you can execute the command like :

---
#rescan-scsi-bus.sh --hosts=1 --luns=2
---

Note : I assume that on host 1/or on HBA 1, lun 2 doesn't exist.

For more details please get help from :

---
#rescan-scsi-bus.s --help

http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Online_Storage_Reconfiguration_Guide/rescan-scsi-bus.html
---

Try :)

How to list out number of files inside each directory?

I developed following script and used it :

---
[root@vijay log]# cat ./find_large_small_files.sh
#!/bin/bash
find . -type d -exec ls -ld {} \; &> ./tmpfile
let i=0
for i in `cat ./tmpfile`
do
echo "Directory $i has following no of files : `ls -al $i|wc -l`"
done

Try and modify as per your need. 

what does it mean by "cman expected_votes="1" two_node="1" in cluster.conf ?

For two node clusters ordinarily, the loss of quorum after one out of two nodes fails will prevent the remaining node from continuing (if both nodes have one vote.) Special configuration options can be set to allow the one remaining node to continue operating if the other fails. To do this only two nodes, each with one vote, can be defined in cluster.conf. The two_node and expected_votes values must then be set to 1 in the cman section as follows.

---
cman two_node="1" expected_votes="1"

Basic Idea about GFS file system!

Global File System (GFS) is a shared disk file system for Linux computer clusters. It can maximize the benefits of clustering and minimize the costs.

It does following :

# Greatly simplify your data infrastructure
# Install and patch applications once, for the entire cluster
# Reduce the need for redundant copies of data
# Simplify back-up and disaster recovery tasks
# Maximize use of storage resources and minimize your storage costs
# Manage your storage capacity as a whole vs. by partition
# Decrease your overall storage needs by reducing data duplication
# Scale clusters seamlessly, adding storage or servers on the fly
# No more partitioning storage with complicated techniques
# Add servers simply by mounting them to a common file system
# Achieve maximum application uptime

While a GFS file system may be used outside of LVM, Red Hat supports only GFS file systems that are created on a CLVM logical volume. CLVM is a cluster-wide implementation of LVM, enabled by the CLVM daemon clvmd, which manages LVM logical volumes in a Red Hat Cluster Suite cluster. The daemon makes it possible to use LVM2 to manage logical volumes across a cluster, allowing all nodes in the cluster to share the logical volumes. Red Hat supports it if gfs is deployed on LVM

GULM (Grand Unified Lock Manager) is not supported in Red Hat Enterprise Linux 5. If your GFS file systems use the GULM lock manager, you must convert the file systems to use the DLM lock manager. This is a two-part process.

* While running Red Hat Enterprise Linux 4, convert your GFS file systems to use the DLM lock manager.
* Upgrade your operating system to Red Hat Enterprise Linux 5, converting the lock manager to DLM when you do.

“GFS with a SAN” provides superior file performance for shared files and file systems. Linux applications run directly on GFS nodes. Without file protocols or storage servers to slow data access, performance is similar to individual Linux servers with directly connected storage; yet, each GFS application node has equal access to all data files. GFS supports up to 125 GFS nodes.

GFS Software Components :

gfs.ko : Kernel module that implements the GFS file system and is loaded on GFS cluster nodes.
lock_dlm.ko : A lock module that implements DLM locking for GFS. It plugs into the lock harness, lock_harness.ko and communicates with the DLM lock manager in Red Hat Cluster Suite.
lock_nolock.ko : A lock module for use when GFS is used as a local file system only. It plugs into the lock harness, lock_harness.ko and provides local locking.

The system clocks in GFS nodes must be within a few minutes of each other to prevent unnecessary inode time-stamp updating. Unnecessary inode time-stamp updating severely impacts cluster performance. Need to use ntpd for accurate time with time server.

A) (On shared disk ) : Create GFS file systems on logical volumes created in Step 1. Choose a unique name for each file system. For more information about creating a GFS file system, refer to Section 3.1, “Creating a File System”.
You can use either of the following formats to create a clustered GFS file system:
Initial Setup Tasks:

1. Setting up logical volumes
2. Making a GFS files system
3. Mounting file systems

#gfs_mkfs -p lock_dlm -t ClusterName:FSName -j NumberJournals BlockDevice
or #mkfs -t gfs -p lock_dlm -t LockTableName -j NumberJournals BlockDevice

OR

#gfs_mkfs -p LockProtoName -t LockTableName -j NumberJournals BlockDevice

#mkfs -t gfs -p LockProtoName -t LockTableName -j NumberJournals BlockDevice

B)At each node, mount the GFS file systems. For more information about mounting a GFS file system.

Command usage:

#mount BlockDevice MountPoint

mount -o acl BlockDevice MountPoint
The -o acl mount option allows manipulating file ACLs. If a file system is mounted without the -o acl mount option, users are allowed to view ACLs (with getfacl), but are not allowed to set them (with setfacl).

Note :

Make sure that you are very familiar with using the LockProtoName and LockTableName parameters. Improper use of the LockProtoName and LockTableName parameters may cause file system or lock space corruption.

LockProtoName :
Specifies the name of the locking protocol to use. The lock protocol for a cluster is lock_dlm. The lock protocol when GFS is acting as a local file system (one node only) is lock_nolock.
LockTableName: This parameter is specified for GFS file system in a cluster configuration. It has two parts separated by a colon (no spaces) as follows: ClusterName:FSName

* ClusterName, the name of the Red Hat cluster for which the GFS file system is being created.
* FSName, the file system name, can be 1 to 16 characters long, and the name must be unique among all file systems in the cluster.

NumberJournals:

Specifies the number of journals to be created by the gfs_mkfs command. One journal is required for each node that mounts the file system. (More journals than are needed can be specified at creation time to allow for future expansion.)

EXAMPLE :http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Global_File_System/ch-manage.html

[root@me ~]# gfs_mkfs -p lock_dlm -t alpha:mydata1 -j 8 /dev/vg01/lvol0
[root@me ~]# gfs_mkfs -p lock_dlm -t alpha:mydata2 -j 8 /dev/vg01/lvol1

Before you can mount a GFS file system, the file system must exist , the volume where the file system exists must be activated, and the supporting clustering and locking systems must be started. After those requirements have been met, you can mount the GFS file system as you would any Linux file system.

EXAMPLE : mount /dev/vg01/lvol0 /mydata1

Displaying GFS Tunable Parameters : gfs_tool gettune MountPoint

try :)

PXE-Boot on RHEL-6

. Use Yum utility to Install required rpm
#yum install dhcp tftp-server syslinux httpd nfs-utils system-config-kickstart bind-*

2. Configure Dns server for host name resolution

#cp -p /etc/named.* /var/named/chroot/etc

#cp -p /var/named.* /var/named/chroot/var/named


#rm -rf /etc/named.*

#rm -rf /var/named.*

#cd /var/named/chroot/etc

#vim named.conf
options {
listen-on port 53 { 127.0.0.1; 192.168.0.254; }; <= Define here the ip of dns
listen-on-v6 port 53 { ::1; };
directory
"/var/named";
dump-file
"/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
memstatistics-file "/var/named/data/named_mem_stats.txt";
allow-query { localhost; any; };
recursion yes;
dnssec-enable yes;
dnssec-validation yes;
dnssec-lookaside auto;
/* Path to ISC DLV key */
bindkeys-file "/etc/named.iscdlv.key";
managed-keys-directory "/var/named/dynamic";
};
logging {
channel default_debug {
file "data/named.run";
severity dynamic;
};
};
zone "." IN {
type hint;
file "named.ca";
};
zone “example.com” IN {                 <= Here declare the forward zone
type master;
file “for.zone”;
};
zone “0.168.192.in-addr.arpa” IN {   <= Here declare reverse zone
type master;
file “rev.zone”;
}
:wq

#cd /var/named/chroot/var/named

#cp -p named.localhost f.zone

#cp -p named.loopback r.zone

#vim f.zone
$TTL 1D
@
IN SOA server1.example.com. root.server1.example.com. (
                                                   0;                      serial
                                                   1D;                   refresh
                                                   1H ;                  retry
                                                   1W;                   expire
                                                   3H ) ;                minimum
                     NS      server1.example.com.
server1         A        192.168.0.254
desktop1       A        192.168.0.1
desktop2       A        192.168.0.2
desktop3
:wq

#vim r.zone
$TTL @  IN SOA  server1.example.com. server1.example.com. (
                                                    0;               serial
                                                    1D;            refresh
                                                    1H ;           retry
                                                    1W;           expire
                                                    3H ) ;        minimum
                             NS     server1.example.com.
254                      PTR    server1.example.com.
1                          PTR    desktop1.example.com.
2                          PTR    desktop2.example.com.
3                          PTR    desktop3.example.com.
:wq

#chkconfig named on ; /etc/init.d/named restart
2. Now Configure the dhcp server
#vim /etc/dhcp/dhcpd.conf
default-lease-time 600;
max-lease-time 7200;
allow booting;
allow bootp;
authoritative;
subnet 192.168.0.0 netmask 255.255.255.0 {
range 192.168.0.1 192.168.0.11;
next-server 192.168.0.254;          <= tftp Server ip
filename "pxelinux.0";
}
:wq

#chkconfig dhcpd on;/etc/init.d/dhcpd restart

3. Configure tftp server
#vim /etc/xinetd.d/tftp
disabled = no
:x

Mount RHEL6 OS dvd on /media directory & copy files required for tftp server
#mount /dev/scd0 /media

#cp -rv /media/isolinux/* /var/lib/tftpboot

#cp -rv /usr/share/syslinux/pxelinux.0 /var/lib/tftpboot

#mkdir /var/lib/tftpboot/pxelinx.cfg

#cp /var/lib/tftpboot/isolinux.cfg /var/lib/tftpboot/pxelinux.cfg/default

Make the OS dump
#cp -rv /media/* /var/www/html

#vim /var/lib/tftpboot/pxelinux.cfg/default
                                                                  <= Make this entery at bottom
label RHEL6-32.bit
menu label ^Install RHEL6-32.bit Unattended
menu defult
kernel vmlinuz
append initrd=initrd.img linux ks=http://192.168.0.254/ks.cfg
:wq
4. Create a ks file by the name of ks.cg, to make pxe unattended by using system-config-kickstart & save it in /var/www/html

5. Start the service xinetd, httpd & on the tftp server
#chkconfig xinetd on ; /etc/init.d/xinetd restart

#chkconfig tftp on

#chkconfig httpd on ; /etc/init.d/httpd restart

Now pxe is ready to Install single OS.

ssh-keygen Process

[root@test ~]# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
0d:f3:e2:dc:63:be:c9:dd:d3:0c:6c:16:62:6e:55:0e root@NDC-LVA-ePDSJB
[root@test ~]# cd .ssh/
[root@test .ssh]# lltotal 12
-rw------- 1 root root 1675 Jun  5 11:39 id_rsa
-rw-r--r-- 1 root root  401 Jun  5 11:39 id_rsa.pub
-rw-r--r-- 1 root root 1183 Apr 17 19:09 known_hosts
[root@test .ssh]# ssh-copy-id -i id_rsa.pub  (Remote IP)
root@Remote IP's password:

Now try logging into the machine, with "ssh "Remote IP'", and check in:  .ssh/authorized_keys
to make sure we haven't added extra keys that you weren't expecting.

[root@test.ssh]# ssh Remote IP

Last login: Mon Jun  4 16:18:03 2012 from Local IP

[root@test ~]# cd .ssh/
[root@test .ssh]# lltotal 8
-rw------- 1 root root 401 Jun  5 11:40 authorized_keys
-rw-r--r-- 1 root root 789 Apr  2 16:11 known_hosts

Linux Set Date

This is useful if the Linux server time and/or date is wrong, and you need to set it to new values from the shell prompt.

You must login as root user to use date command.

root@vijay~]# date -s "2 OCT 2006 18:00:00" 

root@vijay~]# date --set="2 OCT 2006 18:00:00"