If you can't login to a server via serial console and you got login: pam_securetty(login:auth): access denied: tty 'ttyS0' is not secure ! in logs then you have to add at the end of the file /etc/securetty the following lines:
# Standard serial ports
ttyS0
ttyS1
For production server I am using a securetty file which is attached to this page.
Files: securetty.zip
Power
[codesyntax lang="bash"]
Lock screen: ctrl + shift + eject Sleep: command + control + eject
[/codesyntax]
Screen
[codesyntax lang="bash"]
Screen capture (whole screen): command + shift + 3 Screen capture (selection): command + shift + 4 Screen capture to clipboard (whole screen): command + control + shift + 3 Screen capture to clipboard (selection): command + control+ shift + 4
[/codesyntax]
Finder
[codesyntax lang="bash"]
Get info: command + control + i
[/codesyntax]
Assumptions
I am assuming that we have two networks linked with a vpn connection (net1: 10.99.0.0/24 and net2: 10.34.132.0/24). Also I am assuming that on net1 is a functional NIS master server.
NIS MASTER: nis1.test.org 10.99.0.10
NIS SERVER: nis2.test.org 10.34.132.195
How to setup a NIS client
If you put a servername in /etc/yp.conf, make sure the server is also in /etc/hosts. Otherwise if your system boots and the network is not yet up or DNS isn't reachable, ypserv cannot resolve the servers in /etc/yp.conf and will hang!
[codesyntax lang="bash"]
vim /etc/hosts
[/codesyntax]
10.99.0.10 nis1.test.org nis1
Install the netbase, portmap and nis packages
[codesyntax lang="bash"]
apt-get install nis
[/codesyntax]
Configure NIS servers
[codesyntax lang="bash"]
vim /etc/yp.conf
[/codesyntax]
domain test-auth server nis1.test.org
Make domain binding persistent
[codesyntax lang="bash"]
vim /etc/defaultdomain
[/codesyntax]
test-auth
Setup 'running' domain
[codesyntax lang="bash"]
nisdomainname test-auth
[/codesyntax]
Update local maps search rules
[codesyntax lang="bash"]
vim /etc/nsswitch.conf
[/codesyntax]
passwd: db files compat nis
group: db files compat nis
shadow: db files compat nis
netgroup: nis
Restart NIS services
[codesyntax lang="bash"]
/etc/init.d/nis stop /etc/init.d/nis start
[/codesyntax]
Make the auth process query NIS
[codesyntax lang="bash"]
vim /etc/passwd
[/codesyntax]
+@gods::0:0:::
+::0:0:::/bin/false
[codesyntax lang="bash"]
vim /etc/group
[/codesyntax]
+:::
Test NIS client setup
[codesyntax lang="bash"]
id user ypwhich
[/codesyntax]
Setup a NIS server slave
[codesyntax lang="bash"]
vim /etc/default/nis :%s/NISSERVER=false/NISSERVER=slave :%s/YPPWDDIR=\/etc/YPPWDDIR=\/etc\/yp :%s/NISMASTER=/NISMASTER=nis1.test.org :wq
[/codesyntax]
Restart NIS server
[codesyntax lang="bash"]
/etc/init.d/nis stop /etc/init.d/nis start
[/codesyntax]
Links:
http://lyre.mit.edu/~powell/debian-howto/nis.html
http://www.server-world.info/en/note?os=Debian_6.0&p=nis
http://www.linuxhelp.in/2010/05/how-to-install-and-configure-nis-server.html
When you want to install linux on a large number of servers kickstart approach is a very good one. But what about hostname?! You have many choices:
Fortunately for you there is a third option: Automatically set the hostname during Kickstart Installation. I wish to take credit for this, but this will be so unfair for the guy which wrote an article about this.
I won't get to long with the story so... let's get started.
The trick is to pass the kernel a parameter and use it in our kickstart file. What if you were to pass a parameter that it doesn't recognize? In most cases, it will probably ignore it, but it will still in the kernel list. We can check kernel parameters by issuing the following command:
[codesyntax lang="bash"]
cat /proc/cmdline
[/codesyntax]
So what if we can pass a parameter with desired hostname to the kernel? With a very simple script we can parse the output of the above command and look for our parameter.
[codesyntax lang="bash"]
#!/bin/sh
echo "network --device eth0 --bootproto dhcp --hostname localhost.localdomain" > /tmp/network.ks
for x in `cat /proc/cmdline`; do
case $x in SERVERNAME*)
eval $x
echo "network --device eth0 --bootproto dhcp --hostname ${SERVERNAME}" > /tmp/network.ks
;;
esac;
done
[/codesyntax]
Here we are looking for SERVERNAME end evaluates that value into a variable. We will then echo the network setup with the variable (which we will use as part of the hostname setup) and redirect into the file under /tmp. Then we will include that file in our installation section.
You may ask yourself what is all about this line:
[codesyntax lang="bash"]
echo "network --device eth0 --bootproto dhcp --hostname localhost.localdomain" > /tmp/network.ks
[/codesyntax]
in the script above?! Well, if you don't pass the SERVERNAME to the kernel, then /tmp/network.ks will not be created and your installation will fail.
So this is my kickstart file for a minimal CentOS 6.3 installation:
install
firewall --disabled
url --url="ftp://ftp.ines.lug.ro/centos/6.3/os/i386"
network --bootproto=dhcp --device=eth0
rootpw --iscrypted YOUR_ENCRYPTED_PASSWORD
text
%include /tmp/network.ks
keyboard us
lang en_US
selinux --disabled
skipx
logging --level=info
reboot
timezone --utc Europe/Bucharest
bootloader --location=mbr --driveorder=sda,sdb --append="console=tty0 console=ttyS0,115200N1"
zerombr
clearpart --all --initlabel
part / --fstype="ext4" --size=10000
part swap --fstype="swap" --size=8000
part pv.01 --fstype="ext4" --grow --size=1
volgroup vg0 pv.01
logvol /data --vgname=vg0 --percent=90 --name=lv0 --fsoptions=noatime --fstype=ext4 --size=1 --grow
%packages
@core
sed
perl
less
dmidecode
bzip2
iproute
iputils
sysfsutils
rsync
nano
mdadm
setserial
man-pages.noarch
findutils
tar
net-tools
tmpwatch
lsof
python
screen
lvm2
curl
ypbind
yp-tools
smartmontools
openssh-clients
acpid
irqbalance
which
bind-utils
ntsysv
ntp
man
mysql
postfix
chkconfig
gzip
%end
%pre
#!/bin/sh
echo "network --device eth0 --bootproto dhcp --hostname localhost.localdomain" > /tmp/network.ks
for x in `cat /proc/cmdline`; do
case $x in SERVERNAME*)
eval $x
echo "network --device eth0 --bootproto dhcp --hostname ${SERVERNAME}" > /tmp/network.ks
;;
esac;
done
%end
%post
cat > /etc/cron.d/ntpdate < /dev/null 2>&1
EOF
chkconfig ntpd on
chkconfig sshd on
chkconfig ypbind on
chkconfig iptables off
chkconfig ip6tables off
chkconfig yum-updatesd off
chkconfig haldaemon off
chkconfig mcstrans off
chkconfig sysstat off
cat > /etc/motd <> /etc/motd
echo >> /etc/motd
%end
With XenServer it is possible to create backups of VMs, even if they are running. The process is as follows:
Search for the uuid of the VMs to backup
First look for the uuid of the VMs to backup. We don’t want to backup the control domain itself, so we add is-control-domain=false to the vm-list command:
[codesyntax lang="bash"]
xe vm-list is-control-domain=false
[/codesyntax]
Create a snapshot of each (running)
Now we create a snapshot of the VMs we want to backup, replacing the uuid one by one with the ones we found with the previous command. Also replace the name of the snapshot if desired:
[codesyntax lang="bash"]
xe vm-snapshot uuid=8d6f9d81-95b5-2ffb-4ecc-b5e442cc5c22 new-name-label=gb-r7n2-snapshot
[/codesyntax]
This command has a return value: the uuid of the created snapshot. Then we transform the snapshot into a VM to be able to save it to a file, replacing uuid with the return value of the previous command:
[codesyntax lang="bash"]
xe template-param-set is-a-template=false ha-always-run=false uuid=4efd0392-8881-176c-012e-a56e9cb2beed
[/codesyntax]
Save the snapshot to file
In the next step we save the snapshot to a file, replacing uuid with the snapshot uuid and providing a meaningful filename:
[codesyntax lang="bash"]
xe vm-export vm=4efd0392-8881-176c-012e-a56e9cb2beed filename=gb-r7n2-snapshot.xva
[/codesyntax]
Remove the created snapshot
In the final step we delete the snapshot:
[codesyntax lang="bash"]
xe vm-uninstall uuid=4efd0392-8881-176c-012e-a56e9cb2beed force=true
[/codesyntax]
Source: http://www.jansipke.nl/creating-backups-of-running-vms-in-xenserver/
Introduction
This document describes how to install DHCP, DNS and PXE network services on a debian squeeze.
For this tutorial I use a machine that has two network interfaces:
eth0: 10.34.132.149/255.255.254.0 (WAN interface)
eth1: 172.20.30.1/255.255.255.0 (LAN interface)
To install a PXE server, you will need the following components:
DHCP Server
TFTP Server
NFS/FTP/HTTPD server (to store installing files)
Note: DHCP Server will listen only on eth1.
In this tutorial I will use apache2 server.
Install required packages
[codesyntax lang="bash"]
apt-get install tftpd-hpa syslinux dhcp3-server bind9 dnsutils
[/codesyntax]
Configure DHCP Server
[codesyntax lang="bash"]
vim /etc/dhcp/dhcpd.conf
[/codesyntax]
ddns-update-style ad-hoc;
log-facility syslog;
option domain-name "test.org";
option domain-name-servers 172.20.30.1;
option subnet-mask 255.255.255.0;
subnet 172.20.30.0 netmask 255.255.255.0 {
authoritative;
range 172.20.30.10 172.20.30.90; # ip range
option routers 172.20.30.1; # gateway for clients
######
# in case want to deny clients that are not configured in dhcpd uncomment the following line
######
#deny unknown-clients;
allow booting;
allow bootp;
next-server 172.20.30.1; # tftpd server's IP
filename "pxelinux.0";
######
# sample of a client that has mac address reserved on dhcp
######
#host guest1 {
# hardware ethernet 00:0C:29:14:DA:AD;
# fixed-address 172.20.30.15;
#}
######
}
Force DHCP Server to listen only on eth1
[codesyntax lang="bash"]
vim /etc/default/isc-dhcp-server :%s/INTERFACES=""/INTERFACES="eth1"/g :wq
[/codesyntax]
Configure TFTP Server. Change the root directory on startup from /srv/tftp to /tftpboot
[codesyntax lang="bash"]
vim /etc/default/tftpd-hpa :%s/\/srv\/tftp/\/tftpboot/g :wq
[/codesyntax]
Setup TFTP Server network boot files
[codesyntax lang="bash"]
mkdir -p /tftpboot chmod 777 /tftpboot cp -v /usr/lib/syslinux/pxelinux.0 /tftpboot cp -v /usr/lib/syslinux/menu.c32 /tftpboot cp -v /usr/lib/syslinux/memdisk /tftpboot cp -v /usr/lib/syslinux/mboot.c32 /tftpboot cp -v /usr/lib/syslinux/chain.c32 /tftpboot mkdir /tftpboot/pxelinux.cfg
[/codesyntax]
Create PXE menu file
[codesyntax lang="bash"]
vim /tftpboot/pxelinux.cfg/default
[/codesyntax]
default menu.c32
prompt 0
timeout 300
MENU TITLE test.org PXE Menu
LABEL centos6.3_i386
MENU LABEL CentOS 6.3 i386
KERNEL /netboot/centos/6.3/i386/vmlinuz
APPEND console=tty0 console=ttyS0,9600N1 initrd=/netboot/centos/6.3/i386/initrd.img ks=http://172.20.30.1/netboot/centos/6.3/i386/centos6.3-ks.cfg ksdevice=link
Share the internet connection with clients
[codesyntax lang="bash"]
vim /etc/sysctl.conf :%s/#net.ipv4.ip_forward=1/net.ipv4.ip_forward=1 :wq
[/codesyntax]
Apply the settings:
[codesyntax lang="bash"]
sysctl -p
[/codesyntax]
Share internet connection using iptables:
[codesyntax lang="bash"]
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
[/codesyntax]
Configure bind9
[codesyntax lang="bash"]
echo "include \"/etc/bind/bind.keys\"; ">> /etc/bind/named.conf vim /etc/bind/named.conf.options
[/codesyntax]
options {
directory "/var/cache/bind";
auth-nxdomain no; # conform to RFC1035
listen-on-v6 { none; };
forwarders { 8.8.8.8; 8.8.4.4; };
listen-on port 53 { any; };
allow-query { any; };
allow-query-cache { any; };
};
Add the following lines at the end of the named.conf.default-zones
[codesyntax lang="bash"]
vim /etc/bind/named.conf.default-zones
[/codesyntax]
zone "test.org" {
type master;
file "/etc/bind/test.org";
};
zone "30.20.172.in-addr.arpa" {
type master;
file "/etc/bind/30.20.172.in-addr.arpa";
};
[codesyntax lang="bash"]
vim /etc/bind/test.org
[/codesyntax]
$ORIGIN test.org.
$TTL 1H
test.org. IN SOA ns.test.org. root.test.org. (
2012062600 ; serial
12H ; refresh
2H ; retry
1W ; expiry
2D ) ; minimum
test.org. IN NS ns.test.org.
ns.test.org. IN A 172.20.30.1
www10 IN A 172.20.30.10
www11 IN A 172.20.30.11
www12 IN A 172.20.30.12
www13 IN A 172.20.30.13
www14 IN A 172.20.30.14
www15 IN A 172.20.30.15
[codesyntax lang="bash"]
vim /etc/bind/30.20.172.in-addr.arpa
[/codesyntax]
$ORIGIN 30.20.172.in-addr.arpa.
$TTL 2D
@ IN SOA ns.test.org. root.test.org. (
2012062600 ; serial
12H ; refresh
2H ; retry
1W ; expiry
2D ) ; minimum
@ IN NS ns.test.org.
1 IN PTR ns.test.org.
10 IN PTR www10.test.org.
11 IN PTR www11.test.org.
12 IN PTR www12.test.org.
13 IN PTR www13.test.org.
14 IN PTR www14.test.org.
15 IN PTR www15.test.org.
Let's use our DNS server
[codesyntax lang="bash"]
echo "search test.org" > /etc/resolv.conf echo "nameserver 127.0.0.1" >> /etc/resolv.conf
[/codesyntax]
DNS stands for Domain Name System and is a a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. In other words DNS translate human readable hostnames such as test.org into machine readable ip addresses such as 89.36.25.239.
Preliminary notes
- Server Name: ns.test.org
- Server IP: 172.20.30.1/24
Install required software packages
[codesyntax lang="bash"]
yum install bind bind-libs bind-utils
[/codesyntax]
Set BIND service to start on system boot
[codesyntax lang="bash"]
chkconfig named on
[/codesyntax]
Start named service for generating some default configuration files.
/etc/init.d/named start
Note: In case the command above hangs there is an entropy problem. You should install haveged daemon. More details here.
If you don't want to install haveged daemon there is a workaround:
[codesyntax lang="bash"]
rndc-confgen -a -r /dev/urandom
[/codesyntax]
Edit main configuration file and add zone entry of www.test.org
[codesyntax lang="bash"]
vim /etc/named.conf
[/codesyntax]
options {
forwarders { 8.8.8.8; 8.8.4.4; };
listen-on port 53 { any; };
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 { any; };
allow-query-cache { any; };
};
logging {
channel default_debug {
file "data/named.run";
severity dynamic;
};
};
zone "." IN {
type hint;
file "named.ca";
};
zone "test.org" {
type master;
file "test.org";
};
zone "30.20.172.in-addr.arpa" {
type master;
file "30.20.172.in-addr.arpa";
};
Create Zone files which we mentioned in named.conf file
[codesyntax lang="bash"]
cd /var/named vim /var/named/test.org
[/codesyntax]
$ORIGIN test.org.
$TTL 1H
test.org. IN SOA ns.test.org. root.test.org. (
2012062600 ; serial
12H ; refresh
2H ; retry
1W ; expiry
2D ) ; minimum
test.org. IN NS ns.test.org.
ns.test.org. IN A 172.20.30.1
www10 IN A 172.20.30.10
www11 IN A 172.20.30.11
www12 IN A 172.20.30.12
www13 IN A 172.20.30.13
www14 IN A 172.20.30.14
www15 IN A 172.20.30.15
[codesyntax lang="bash"]
vim /var/named/30.20.172.in-addr.arpa
[/codesyntax]
$ORIGIN 30.20.172.in-addr.arpa.
$TTL 2D
@ IN SOA ns.test.org. root.test.org. (
2012062600 ; serial
12H ; refresh
2H ; retry
1W ; expiry
2D ) ; minimum
@ IN NS ns.test.org.
1 IN PTR ns.test.org.
10 IN PTR www10.test.org.
11 IN PTR www11.test.org.
12 IN PTR www12.test.org.
13 IN PTR www13.test.org.
14 IN PTR www14.test.org.
15 IN PTR www15.test.org.
Restart named service
[codesyntax lang="bash"]
/etc/init.d/named restart
[/codesyntax]
Update /etc/resolv.conf file
[codesyntax lang="bash"]
echo "search test.org" > /etc/resolv.conf echo "nameserver 127.0.0.1" >> /etc/resolv.conf
[/codesyntax]
Source: http://www.broexperts.com/2012/03/linux-dns-bind-configuration-on-centos-6-2/
Introduction
How to check entropy level:
[codesyntax lang="bash"]
watch -n1 cat /proc/sys/kernel/random/entropy_avail
[/codesyntax]
If the value is to low (around 100) install haveged daemon
How to install haveged on Linux
Debian
[codesyntax lang="bash"]
apt-get install haveged
[/codesyntax]
CentOS
haveged daemon is available for CentOS via EPEL repository.
First, we download and import the GPG keys for EPEL software packages:
[codesyntax lang="bash"]
wget http://ftp.riken.jp/Linux/fedora/epel/RPM-GPG-KEY-EPEL-6 rpm --import RPM-GPG-KEY-EPEL-6 rm -f RPM-GPG-KEY-EPEL-6
[/codesyntax]
Download EPEL repository for 32-bit CentOS
[codesyntax lang="bash"]
wget http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-7.noarch.rpm
[/codesyntax]
Install EPEL repository on 32-bit CentOS
[codesyntax lang="bash"]
rpm -ivh epel-release-6-7.noarch.rpm
[/codesyntax]
You can start install and use EPEL the repository to install the software packages, input yum command like follows:
[codesyntax lang="bash"]
yum --enablerepo=epel install haveged
[/codesyntax]
Introduction
Citrix XenServer 5.5, 5.6 and 6.0 are based on CentOS 5.4, but the smartmontools package is not available in the default Citrix repository, so it can't be installed with yum install smartmontools (as it would be possible with any other CentOS distribution).
Installation
It is probably safest to use the same versions that were in the original CentOS 5.4 distribution. Since that release is no longer the latest, we have to go to an archive server to find the packages. The packages listed below are actually used in other CentOS releases too, so these are probably the latest versions anyway.
[codesyntax lang="bash"]
wget http://vault.centos.org/5.4/os/i386/CentOS/mailx-8.1.1-44.2.2.i386.rpm
wget http://vault.centos.org/5.4/os/i386/CentOS/smartmontools-5.38-2.el5.i386.rpm
rpm -hiv smartmontools-5.38-2.el5.i386.rpm mailx-8.1.1-44.2.2.i386.rpm
[/codesyntax]
Checking the disk status
We can now retrieve the disk status using:
[codesyntax lang="bash"]
smartctl -d ata -a /dev/sda
[/codesyntax]
The most important fields are: SMART overall-health self-assessment test result - that should always have a value of PASSED. Other important fields are:
Also check out the columns VALUE WORST THRESH. For each attribute, the current value of the field should never be lower than the threshold defined by the manufacturer.
Automatic monitoring of disk drives
The smartd daemon handles automatic testing for all drives, logs any status changes in /var/log/syslog or /var/log/messages and sends a status email in case of a problem (if mail is enabled, see below). It is configured in the file /etc/smartd.conf.
The following lines will run a short test every day between 02:00 and 03:00, and a long test on every Saturday between 03:00 and 04:00. If there is a problem, send an email to the configured address. The -M test option will send a test email whenever the smartd daemon is started.
The DEVICESCAN line would normally cause default test runs for all disks that smartd finds, but does not work on my system for some reason. So it is commented out and the tests will only run for explicitly listed devices.
[codesyntax lang="bash"]
/dev/sda -d ata -a -s (S/../.././02|L/../../6/03) -t -m user@example.com
/dev/sdb -d ata -a -s (S/../.././02|L/../../6/03) -t -m user@example.com
#DEVICESCAN -H -m root
[/codesyntax]
After any change to the /etc/smartd.conf file the smartd daemon should be restarted:
[codesyntax lang="bash"]
/etc/init.d/smartd restart
[/codesyntax]
Enabling email on Citrix XenServer
Citrix XenServer is not configured to run a mail server. Therefore without further configuration smartd might attempt to send out warning emails in case anything fails, but no mails will actually receive their destination.
It is fortunately not necessary to install a full-blown email package. XenServer comes with ssmtp preinstalled, which simply forwards emails to a real mail server.
To enable mail sending on Citrix XenServer, set up /etc/ssmtp/ssmtp.conf. You need to provide a real mail server and the local domain name.
#
# /etc/ssmtp.conf -- a config file for sSMTP sendmail.
#
root=postmaster
mailhub=relay.example.com
rewriteDomain=nxen01.example.com
hostname=nxen01.example.com
After setting up /etc/ssmtp/ssmtp.conf, send a test email from the console to make sure that the email gets through:
[codesyntax lang="bash"]
echo "this is a test mail" | mailx -s "Test mail" user@example.com
[/codesyntax]
If you are using the -M test option to a /etc/smartd.conf device definition, you can also restart the smartd daemon to have it send out test emails.
Create a new RAID array
Create (mdadm --create) is used to create a new array:
[codesyntax lang="bash"]
mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb2
[/codesyntax]
or using the compact notation:
[codesyntax lang="bash"]
mdadm -Cv /dev/md0 -l1 -n2 /dev/sd[ab]1
[/codesyntax]
/etc/mdadm.conf
/etc/mdadm.conf or /etc/mdadm/mdadm.conf (on debian) is the main configuration file for mdadm. After we create our RAID arrays we add them to this file using:
[codesyntax lang="bash"]
mdadm --detail --scan >> /etc/mdadm.conf
[/codesyntax]
or on debian
[codesyntax lang="bash"]
mdadm --detail --scan >> /etc/mdadm/mdadm.conf
[/codesyntax]
Remove a disk from an array
We can’t remove a disk directly from the array, unless it is failed, so we first have to fail it (if the drive it is failed this is normally already in failed state and this step is not needed):
[codesyntax lang="bash"]
mdadm --fail /dev/md0 /dev/sda1
[/codesyntax]
and now we can remove it:
[codesyntax lang="bash"]
mdadm --remove /dev/md0 /dev/sda1
[/codesyntax]
This can be done in a single step using:
[codesyntax lang="bash"]
mdadm /dev/md0 --fail /dev/sda1 --remove /dev/sda1
[/codesyntax]
Add a disk to an existing array
We can add a new disk to an array (replacing a failed one probably):
[codesyntax lang="bash"]
mdadm --add /dev/md0 /dev/sdb1
[/codesyntax]
Verifying the status of the RAID arrays
We can check the status of the arrays on the system with:
[codesyntax lang="bash"]
cat /proc/mdstat
[/codesyntax]
or
[codesyntax lang="bash"]
mdadm --detail /dev/md0
[/codesyntax]
The output of this command will look like:
[codesyntax lang="bash"]
cat /proc/mdstat
[/codesyntax]
Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[0]
104320 blocks [2/2] [UU]
md1 : active raid1 sdb3[1] sda3[0]
19542976 blocks [2/2] [UU]
md2 : active raid1 sdb4[1] sda4[0]
223504192 blocks [2/2] [UU]
here we can see both drives are used and working fine - U. A failed drive will show as F, while a degraded array will miss the second disk _
Note: while monitoring the status of a RAID rebuild operation using watch can be useful:
[codesyntax lang="bash"]
watch -n1 cat /proc/mdstat
[/codesyntax]
Checking a linux MD raid array
In this example my RAID array will be /dev/md0
[codesyntax lang="bash"]
cd /sys/block/md0/md echo check >sync_action watch -n1 cat /proc/mdstat
[/codesyntax]
OR:
[codesyntax lang="bash"]
/usr/share/mdadm/checkarray -a /dev/md0 watch -n1 cat /proc/mdstat
[/codesyntax]
Note: if you receive the following error message:
[codesyntax lang="bash"]
checkarray: W: array md0 in auto-read-only state, skipping...
[/codesyntax]
Then you should do this:
[codesyntax lang="bash"]
mdadm --readwrite /dev/md0
[/codesyntax]
Stop and delete a RAID array
If we want to completely remove a raid array we have to stop if first and then remove it:
[codesyntax lang="bash"]
mdadm --stop /dev/md0 mdadm --remove /dev/md0
[/codesyntax]
and finally we can even delete the superblock from the individual drives:
[codesyntax lang="bash"]
mdadm --zero-superblock /dev/sda
[/codesyntax]
Finally in using RAID1 arrays, where we create identical partitions on both drives this can be useful to copy the partitions from sda to sdb:
[codesyntax lang="bash"]
sfdisk -d /dev/sda | sfdisk /dev/sdb
[/codesyntax]
(this will dump the partition table of sda, removing completely the existing partitions on sdb, so be sure you want this before running this command, as it will not warn you at all).
There are many other usages of mdadm particular for each type of RAID level, and I would recommend to use the manual page (man mdadm) or the help (mdadm --help) if you need more details on its usage. Hopefully these quick examples will put you on the fast track with how mdadm works.
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