If you found any of my tips useful and you'd like to say "thanks", why not invite me to a virtual cup of joe to keep the little grey cells percolating.
Over 80% is running on some form of Linux – so does your Mac and you iPhone. Sometimes we have to get our hands dirty on the command line – it makes you feel like a proper hacker.
Here are some pointers I picked up on my journey.
yum can help us here. This should do the trick:
#yum list installed
If you’re interested in a particular package, you can pipe a search string into grep and only list filtered results:
#yum list installed | grep "yum" keyutils-libs.i686 1.4-4.el6 @anaconda-CentOS-201303020136.i386/6.4 yum.noarch 3.2.29-40.el6.centos yum-metadata-parser.i686 yum-plugin-fastestmirror.noarch
The search string doesn’t even need to be in quotes, and partials work fine too.
Two commands come to the rescue: ip and ifconfig. Either does the trick:
#ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:19:99:0D:D2:58
inet addr:87.106.181.234 Bcast:87.106.181.234 Mask:255.255.255.255
inet6 addr: fe80::219:99ff:fe0d:d258/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:14022830 errors:1 dropped:0 overruns:0 frame:1
TX packets:17605482 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:6842851425 (6.3 GiB) TX bytes:22015650673 (20.5 GiB)
Interrupt:225 Base address:0x2000
Slightly more parameters with ip, and slightly less output:
#ip addr show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:19:99:0d:d2:58 brd ff:ff:ff:ff:ff:ff
inet 87.106.181.234/32 brd 87.106.181.234 scope global eth0
inet6 fe80::219:99ff:fe0d:d258/64 scope link
valid_lft forever preferred_lft forever
The output on the second line is the IP address (in our example 87.106.181.234).
Once you’ve created an EBS Volume in the AWS web interface and attached it to an EC2 instance, how do you actually use it on your virtual server?
Here’s how! The following commands assume you’re logged into your system as root. I’ve created a 13GB volume and attached it to my running instance.
Let’s get a quick overview of our file system before we get started:
# df -h Filesystem Size Used Avail Use% Mounted on /dev/xvde 7.9G 1.7G 5.9G 23% / tmpfs 296M 0 296M 0% /dev/shm
Looks like right now I’ve only got one 8GB partition available. Let’s take a look at what else may be available to mount:
# fdisk -l Disk /dev/xvde: 8589 MB, 8589934592 bytes 255 heads, 63 sectors/track, 1044 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Disk /dev/xvdj: 14.0 GB, 13958643712 bytes 255 heads, 63 sectors/track, 1697 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000
The second block tells us that an unused partition is at our disposal. That’s good news – let’s see how we can make that available for storage.
Depending on your Linux distribution, what you see in Amazon isn’t what your file system sees. Amazon may have told you that you’ve attached a volume as /dev/sdf, but your kernel may give it a different name – as seen with fdisk command above. Here’s another way to see your partitions using lsblk:
# lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT xvde 202:64 0 8G 0 disk / xvdj 202:144 0 13G 0 disk
We can see that xvde is mounted on root (or /) and xvdj is not – that’s our new EBS volume. Let’s attach it so we can use it.
Before we do, we may have to format the partition. If you’ve used this EBS Volume before and it already contains data you don’t want to do this as it will – obviously – erase all your data. In our case however it’s a fresh volume so it needs formatting. This will take a moment, depending on the size of your volume:
# mkfs -t ext3 /dev/xvdj Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=0 blocks, Stripe width=0 blocks 851968 inodes, 3407872 blocks 170393 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=3489660928 104 block groups 32768 blocks per group, 32768 fragments per group 8192 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208 Writing inode tables: done Creating journal (32768 blocks): done Writing superblocks and filesystem accounting information: done This filesystem will be automatically checked every 35 mounts or 180 days, whichever comes first. Use tune2fs -c or -i to override.
Nice! The above command formats our volume as third extended filesystem and it’s now ready for use.
Let’s create a directory so that Linux can speak to the new partition. I’ll call mine “/storage” and mount the partition to it:
# mkdir /storage # mount /dev/xvdj /storage
No news means good news. Let’s check what our file system looks like now:
# df -h Filesystem Size Used Avail Use% Mounted on /dev/xvde 7.9G 1.7G 5.9G 23% / tmpfs 296M 0 296M 0% /dev/shm /dev/xvdj 13G 161M 12G 2% /storage
Smashing! 12GB of usable storage has been attached to our EC2 instance, ready to be populated with tons of files.
EBS Volumes are persistent, which means that whatever is saved on it will remain intact, even if you terminate our instance. In fact, you can detach your volume and attach it to another running instance and start using your data. Here’s how:
Rather than “force detaching” the volume in the web interface, let’s ask our instance to unmount it first. This is the equivalent of saying to Windows “Safely Eject my USB stick”:
# umount /storage # df -h Filesystem Size Used Avail Use% Mounted on /dev/xvde 7.9G 1.7G 5.9G 23% / tmpfs 296M 0 296M 0% /dev/shm
Make sure you’re not cd’d into your directory or you’ll get an error message that it’s “in use”. I’m also checking that I no longer have /storage in my file system.
You can now attach this volume to another instance, mount it again and see all your data on another server.
Is this cool or what?
Need to find a file on your system? Look no further than the excellent find command line tool.
Here’s how to use it:
find / -name 'yourfilename.extension'
This brings up a list of every file whose name matches “yourfilename.extention”. Wildcards are allowed, so you could list every .log file on the system like this:
find / -name '*.log'
The forward-slash just after find command lets you specify where to start your search. So forward-slash (i.e. ‘/’) means you’re looking everywhere. You can specify a directory like this:
find /path/to//your/directory -name '*.log'
Find is a complex command – have a look at what else it has to offer:
Creating a ZIP file on your Mac is really easy: select a few files in Finder, right-click on those and select “Compress…”. It’s the equivalent of selecting “Send to ZIP Folder” under Windows.
But Mac OSX does something rather bizarre when creating ZIP files: it adds several unnecessary, unwanted and un-called-for files starting with __MACOSX. This drives PC users nuts – and believe me, it drives Mac users nuts too.
Thankfully there is a relatively easy way to remove those files. This may not always be necessary, but if you require a “clean” ZIP file, here’s what you can do.
First, create your ZIP via the finder – like you always do. Next, open Terminal and cd into the directory where your ZIP file is located. If it’s a long path, just type “cd “, then drag the folder into Terminal (less typing is always good).
Now type the following:
zip -d your-archive.zip "__MACOSX*"
And that should do it. This command (zip) will remove everything (-d) starting with __MACOSX from your ZIP file (your-archive.zip).
To verify, type the following:
unzip -l your-archive.zip
This will simply list the contents of your-archive.zip.
Alternatively there is a utility called YemuZip: http://www.yellowmug.com/yemuzip/
Or just use a PC 
.DS_Store is another one of those annoying Mac files – it can be removed the same way.
…or you can alternatively download and use free Keka archiver, which contains option to simply “Exclude Mac resource forks”.
Keka allows you to compress to those formats: 7z, Zip, Tar, Gzip, Bzip2, DMG, ISO
and it also unpacks all those: RAR, 7z, Lzma, Zip, Tar, Gzip, Bzip2, ISO, EXE, CAB, PAX, ACE (PPC)
You can set Keka as a default OS X compressor/decompressor and one thing that I miss in OS X compression utility the most – you can set method of compression (store, fast, normal, best/slow), allows you to split archives to volumes and also set up archive passwords. And even more…
Check it out for sure 
Sure will, thanks for the tip! Here’s the link:
http://www.kekaosx.com/en/
You can use Long Path Tool if you are finding issues related to your long path files.
Every once in a while it can happen happen that use use “yum update” to update your Linux system.
Usually this works without a hitch, but you may have come across a message such as this:
Setting up Install Process
Resolving Dependencies
There are unfinished transactions remaining. You might consider running yum-complete-transaction first to finish them.
The program yum-complete-transaction is found in the yum-utils package.
But what does this mean, and how do we alleviate this?
I’ve just ordered a new Dynamic Cloud Server with 1&1 with a total of 800GB disk space. They rock, but they come with a minor inconvenience: due to the way these server instances are allocated, 1&1 do not automatically extend the partition for you – so you can’t actually start using the full amount you’ve ordered.
Here’s how to make use of the full disk space on a current file system:
This is a step-by-step guide on how to replicate an existing MySQL server. The server is live and contains data and needs a constant backup companion.
Many tutorials focus on how to setup replication when no data is present on the system. That’s an ideal solution if you’re building a new setup, but in case you’ve got a server that already has data present then here’s how to accomplish the this:
I’ve done this several times and always forgot to take some notes – until today. Without further ado, let’s replicate MySQL.
A couples of errors:
mysql# release lock; -> this should be mysql# unlock tables;
root# mysql -p > everything.sql -> this should be root# mysql -p < everything.sql
And some code error:
mysql# CREATE USER 'replicator'@'%' IDENTIFIED BY '***';
mysql# GRANT REPLICATION SLAVE ON * . * TO 'replicator'@'%'
IDENTIFIED BY '***' WITH MAX_QUERIES_PER_HOUR 0
MAX_CONNECTIONS_PER_HOUR 0 MAX_UPDATES_PER_HOUR 0
MAX_USER_CONNECTIONS 0 ;
Remove the "" parts
Thanks Fabrizio,
you’re a life saver – not sure how I got those rather crucial commands wrong there. I’ve updated the article. Much appreciated!
Today was a rather exciting day for me: I’ve successfully turned my aging Samsung NC10 Netbook into an internal server in our office.
I bought the little guy in 2009 and he’s been my trusty companion on many jobs before I got an iPad. He still works fine, even though Windows XP was getting weird of late – and admittedly I hadn’t even turned him on in over 8 months.
Now my trusty pal is running CentOS 6.4 while sitting quietly in a corner next to the modem, serving as an internal Linux server. This is great for testing and automated backups – and in the same spirit as playing with a Raspberry Pi (in a much neater battery powered package).
Refreshing the NC10 wasn’t a picnic though, and some of the steps are rather involved. Here are my notes, in case I either have to do it again or you want to follow along.
On both CentOS and Red Hat Linux systems you can easily create new user accounts with their own home directories.
Here’s how you do this from the command line. I’m assuming you’re logged in as root, and the new user we’d like to create is called “testuser”:
useradd testuser
Let’s give our testuser a password so s/he can login to the system via SSH:
passwd testuser
This will prompt for a new password (twice), followed by the message that “all authentication tokens have been updated”. Which is nice.
You can now login as “testuser” with your designated password. Testuser’s home directory is located here:
/home/testuser
That’s all there’s to it – congratulations on creating a new user on your system
aliceten, 
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