SA Cheat Sheet

I need a place to jot down some general configuration helps and command syntax. Hence, the SA Cheat Sheet.
(**Primarily for VMware, RHEL and CentOS systems)
(**This is a living document and will be updated as I find more tips I need to remember)


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Using tar to copy directories and files to another location on the same server or a different server.
Example to copy /opt/copyme to /data/copyme on the same server:

$ cd /opt
$ tar cvfp - copyme | (cd /data && tar xvfp -)

Example to copy a user bart’s home directory to a different server:

$ cd /home
$ tar cvfp - bart | ssh root@targetserver ‘cd /home && tar xvfp -’

Clear out all messages in the postfix queue

$ postsuper -d ALL

Show what is using virtual memory.

$ ps -e -o pid,vsz,comm= | sort -n -k 2

A note about xargs.
If you have two arguments, say r1.txt and r2.txt from the command “ls r*.txt”:

$ ls r*.txt | xargs rm

will execute the rm command this way...
rm r1.txt r2.txt

However,

$ ls -r*.txt | xargs -i{} rm {}

will execute the args separately, this way...
rm r1.txt
rm r2.txt

Using ssh keys for no-password root login to ESX hosts.
For ESX 5.x, place the public key (id_dsa.pub or id_rsa.pub) in:

<ESX 5 host>:/etc/ssh/keys-root/authorized_keys

For ESX 4.x, place the public key in:

<ESX 4 host>:/.ssh/authorized_keys

Various ways of listing disks / storage on a server.
fdisk - list disks

$ fdisk -l

lsscsi - list SCSI devices and various info (rpm lsscsi)

$ lsscsi

pvscan - list physical volumes that are part of the LVM

$ pvscan

Scan a live server for new scsi disk using scsi-rescan (included in sg3_utils rpm)

$ scsi-rescan

After running scsi-rescan, new disks will show up with “fdisk -l” and can be added to LVM with the pvcreate utility.

Remounting a read only file system as read write:

mount -o remount <file system>

Example:

$ mount -o remount /var

Show server port information and connected / listening ports.
netstat (included with net-tools rpm)

$ netstat -putlan

lsof (included with lsof rpm)

$ lsof -i

$ lsof -i -P #shows what is using which ports but doesn’t convert port numbers to names

$ lsof -i :80 #shows what is using port 80

Remove the virbr0 interfaces:

$ virsh net-destroy default
$ virsh net-undefine default
$ service libvirtd stop
$ chkconfig libvirtd off

Search and replace in vi (starting at the first line through the entire file):

:1,$s/<text to match>/<replace with this>/g

Mail .forward and /etc/aliases

The aliases defined in /etc/aliases take precedence over user's .forward file settings.