# mount -n -o remount /

If /etc/fstab is wrong, you must give the device name and possibly the
type, too: e.g.

# mount -n -o remount -t ext4 /dev/sda3 /

crm_mon

Migrate all resources to another node:

crm resource migrate rg_main <fqdn_node_name>

Take node offline and online (be careful, this sets a ‘prefer’ to the other node to force a transition, which may or may not get removed afterwards):

crm node standby
crm node online

Start and stop all resources (warning, this will take them completely offline, NOT migrate):

crm resource stop rg_main
crm resource start rg_main

Show configuration:

crm configure show

If resources are stuck in ‘(unmanaged) FAILED’ state, e.g. due to a failed stop action, you can clear it out:

crm_resource -P

Be careful — this could trigger a migration if the stuck resources were preventing one. Make sure you’re ready for one.

Monitor the cluster status along with fail counts:

crm_mon --failcount

One-shot status output:

crm status

Check DRBD status:

cat /proc/drbd

DRBD split-brain cleanup on secondary node:

drbdadm disconnect main
drbdadm -- --discard-my-data connect main

DRBD split-brain cleanup on primary node:

drbdadm disconnect main
drbdadm primary main
drbdadm connect main

Scheduler optimizing on large arrays (untested):

echo deadline > /sys/block/sdb/queue/scheduler
echo 0 >  /sys/block/sdb/queue/iosched/front_merges
echo 150 > /sys/block/sdb/queue/iosched/read_expire
echo 1500 > /sys/block/sdb/queue/iosched/write_expire

1. Exchange Management Console -> Server Configuration -> Hub Transport

2. New Receive Connector

* Set remote network to the IP or range you want to allow relay from (default is any IP so watch out here)
* “Externally Secured” authentication
* “Exchange Servers” permission group
* All other options disabled

Error happened when generating Download Link.
Please try again or Contact administrator.
(ERROR:mkdir)

A quick and dirty way to increase the limit (and overall performance of the system) is to add the dir_index flag to the ext filesystem, then reindex:

tune2fs -O dir_index /dev/sda3
updatedb &

yum -y install ipmitool
modprobe ipmi_devintf
ipmitool -I open user set password 2 ADMIN

http://www.openwall.com/phpass/

Good reading for password hashing in general.

http://www.openwall.com/articles/PHP-Users-Passwords

NOTE1: This won’t work on Cpanel servers due to tmp restrictions.

NOTE2: Specify an alternative (e.g newer) GeoIPASNum.dat file with the –geo option.

wget http://djlab.com/stuff/asnum
chmod +x asnum
./asnum

Example output:

[root@mx1 ~]# ./asnum
(18) | RFC1918 or BOGON
(11) | AS29889 Fast Serv Networks, LLC
(4) | AS3320 Deutsche Telekom AG
(2) | AS7922 Comcast Cable Communications, Inc.

Quick and (very) dirty cron script

#!/bin.sh
#/root/doasnum.sh
#*/5 * * * * /root/./doasnum.sh >> /var/log/asnum.log

thedate=`date`
echo "***********************"
echo $thedate
/root/asnum
echo "***********************"

Don’t forget to rotate the logs.

#/etc/logrotate.d/asnum
/var/log/asnum.log
{
        rotate 7
        daily
        missingok
}

1. Use PAR with PAR::Filter::Obfuscate or PAR::Filter::Crypto

2. Use Filter::Crypto::CryptFile (requires certain modules installed on target system)

3. Encrypt modules with Module::Crypt.

1. Boot into rescue mode (iso, pxe, ect).

2. Create partitions with ‘fdisk /dev/sda’. Type 83 for non-RAID fs, 82 for swap, type fd in the case of RAID (all partitions). Flag boot partition as bootable.

In the case of SSD, add -S 32 -H 32 to the fdisk command and start the first partition on sector 2 for proper alignment.

If using RAID, duplicate the partition table after creating it on the first disk:

dd if=/dev/sda of=/dev/sdb bs=1 count=64 skip=446 seek=446

2. Create RAID array (if applicable).

# For SSD, add: --chunk=128
mdadm --create /dev/md0 -e 0.90 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1  ## /boot
mdadm --create /dev/md1 -e 0.90 --level=1 --raid-devices=2 /dev/sda2 /dev/sdb2  ## Swap
mdadm --create /dev/md2 -e 0.90 --level=1 --raid-devices=2 /dev/sda3 /dev/sdb3  ## /

3. Create filesystems

For spin disk:

mkfs.ext3 /dev/md0 # /dev/sda1 for non-RAID
mkfs.ext3 /dev/md2 # /dev/sda3 for non-RAID

For SSD (non RAID):

mkfs.ext3 -b 1024 -E stride=128,stripe-width=128 -O ^has_journal /dev/sda1
mkfs.ext3 -b 1024 -E stride=128,stripe-width=128 -O ^has_journal /dev/sda3

For SSD (RAID):

mkfs.ext3 -b 1024 -E stride=128,stripe-width=256 -O ^has_journal /dev/md0 ## stripe-width = stride x N disks
mkfs.ext3 -b 1024 -E stride=128,stripe-width=256 -O ^has_journal /dev/md2 ## stripe-width = stride x N disks

4. Mount filesystems

mkdir /mount
mount /dev/md2 /mount  ## /dev/sda3 for non-RAID
mkdir {/mount/boot,/mount/dev,/mount/sys,/mount/proc,/mount/tmp}  
mount /dev/md0 /mount/boot ## /dev/sda1 for non-RAID

5. Sync filesystems with Rsync over SSH (Ex: 1.2.3.4 is source machine)

rsync -aHxv root@1.2.3.4:/* /mount --exclude=/dev --exclude=/proc --exclude=/sys --exclude=/tmp
rsync -aHxv root@1.2.3.4:/boot/* /mount/boot --exclude=/dev --exclude=/proc --exclude=/sys --exclude=/tmp  ## Only if /boot is on separate partition in source machine

If applicable: stop mysql on the source machine and resync the databases to prevent corruption:

rsync -aHxv root@1.2.3.4:/var/lib/mysql/* /mount/var/lib/mysql

6. Update mdadm.conf

mdadm --examine --scan > /mount/etc/mdadm.conf

7. Update fstab (if needed)

vi /mount/etc/fstab

8. Install bootloader

grub
root (hd0,0)
setup (hd0)
root (hd1,0)  ## for RAID
setup (hd1)  ## for RAID
exit

9. Optional: change IP address if both machines need to be online

vi /mount/etc/sysconfig/network-scripts/ifcfg-eth0

10. Cross fingers, reboot

reboot