Listing all available package versions with yum

Sometime I needs to install an older flavour of a package.  You can list these with yum and install a specific version, e.g.

yum --showduplicates list mod_ssl
yum install mod_ssl-2.2.3-53.el5

Tracing Redirects with curl

I quite often need to debug rewrites and redirects and with curl this is quite easy.

curl -I -L "http://somewhere.com"

also you can add the -k option to ignore invalid certificate errors

SSH Piping between remote servers

SSH is without doubt my favourite command line tool. Today I needed to transfer a file between two hosts that I could SSH to, but could not SSH to each other. This is really simple with a bit of standard UNIX piping.

ssh hostA cat somescript.sh | ssh hostB "cat > somescript.sh"

Job done.

iproute2 cheat sheet

Ok so apparently ifconfig is either deprecated or old fashioned and your supposed to use the 'ip' command instead. Turns out it's really nice and I prefer it to ifconfig,route,already.

Here's some examples:

ip addr - equivalent to ifconfig

ip addr show eth0 - same as above just show eth0

ip ro - show routing table

ip route add default via 192.168.0.254 - set the default gateway

ip addr add 192.168.0.5/24 brd + dev eth0 label eth0:0 - set an ip alias on eth0 and call it eth0:0

ip neigh - show the arp table

Disable a yum repository while running yum update

I wanted to run all updates from the RHEL repositories, but not the rpmforge and WAN Disco ones. Easy.

sudo yum check-update --disablerepo=rpmforge --disablerepo=WANdisco-dev

Resize images on the command line

I've recently been buying allot of digital downloads and it seems a waste that the album art encoded into the track is often 1500x1500 and taking up valuable disk space.

A quick blast with Graphics Magick solves all

gm mogrify -scale 25% Artwork.jpg

Rsync happiness

I recently got around to setting up a backup of my data. I decided rather than using something like Drop Box (which i'm sure is great) I'd keep things simple and set up a new EBS volume on my EC2 box and rsync my data there.

Here was the initial command I used to get the first sync in place manually.

rsync -arvzh --progress -e 'ssh -i path to pub key' /dir/to/backup user@host:/backup/dir/here

A quick review of the flags

-a archive mode (preserve timestamps)

-r recurse into directories

-v verbose

-z compress data during transfer

-h output in human readable format

--progress show a nice progress meter (won't want this in script)

-e specify remote shell and put any further args in quotes