howto: make grub boot a specific stanza only once on the next boot for centos 6.x

sometimes when experimenting, we need a certain grub config/stanza. but what do we do if the stanza is not 100% there yet? well normally it means we have to reboot the box and manually select the healthy stanza and boot it.

however there are some scenarios that dont make this a reasonable approach. stanalone servers with no consoles attached.

so what we want is to tell grub to boot our new stanza only once and this is the command to do it

echo "savedefault --default=N --once" | grub --batch

where N is the number of the stanza you are working on.

howto: modify the partitions labels

disk labels are useful. the disk identifier used to be in the /dev/sdb format. but that device name is interchangeable with the other disks. so then it was best to use uuid but the uuid would depend on what the motherboard called its device. the above methods are not persistent. meaning it is not guaranteed across reboots and across different computers. so the best method is to use disk labels.

lets start off first with reading disk labels

how to add a swap file

lets assume, your server is setup in the cloud. and in the cloud RAM costs quite a bit. but the minimum configuration server provided has a lot of disk space. ssd disk space. an ssd disk is pretty fast. and you dont need all that ssd disk space for data. and you would like to use that fast disk space to expand your swap memory.

well read on!

learning from history

i always thought the history command wasnt configurable. boy was i wrong

so i was able to identify exactly when each command in history was run by using the command

export HISTTIMEFORMAT="%Y-%m-%d %T  "; history

where HISTTIMEFORMAT follows the date command's syntax.

more reading material can be found here

some file management commands

sometimes we need to know how to manage files from the command line. the usual cohort includes cp, rm and mv but what kind of extended commands are out there for us to use?

fdupes is a program that finds duplicate files and it is available in the epel repo

fdupes -R -d /path/to/dir1 /path/to/dir2

where -R tells it to search recursively and -d to delete (it asks you first which to keep)

cp -rn /path/1 /path/2

where -r is recursive, meaning copy directories and -n means no clobber, meaning do not overwrite

how to disable fprintd, the fingerprint daemon

you are here because you want to disable the fprintd ; fingerprint daemon on your machine. short answer is you cant.

long answer is it is isnt a service that you can enable or disable it is called by dbus when there is a need for it. i did discover a method to disable that part of it in this thread but you know what? i like a suggestion in there too

yum -y erase fprintd

and i am a happy camper! :D

how to do bluetooth pairing on centos

this is a story of a phone that wanted to pair with a centos box via bluetooth.

the centos box has a bluetooth dongle

the steps are:

1. install the bluetooth stack and python dependencies

yum -y install pygobject2 bluez

2. get simple-agent, the python script that pairs the bluetooth devices together

wget https://gitorious.org/bluez/mainline/raw/a04f48420ffc2c1a33e743d5075f24809161b2fd:test/simple-agent
chmod +x simple-agent

3. get the mac address of the phone

hcitool scan

4. set the pin for your centos box

dynamic dns and ddclient

to access my home computers, i use dynamic dns or ddns for short. i have been using dynamic dns from before the days they were a commercial dns provider. then the started selling dns services and began limiting ddns hosts. then they made them a max of 3 and then a week ago, they cut off the legs on the free ddns service.

installing a hp wifi enabled printer

this is just a quick note about installing a wifi enabled hp printer on fedora (20)initial set up must first be initiated by direct USB cable via

hp-setup

hp-setup is installed as part of the hplip* packages. it needs the hplip-gui package specifically.

once the printer is configured for wireless networking (aka IP), you can use system-config-printer to add the wireless printer. but before you do that you must open up your firewall with

how to: Installing ESXi 5.5 on less than 2GB RAM

you may know i am trying to set up an esx lab at home. i was trying to do it with nested virtualisation but it wasnt working out very well so instead i dig up an old hp 7800 desktop that i had and slid the cd in.

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