Ubuntu – Ubuntu Desktop Installation Partition Sizing Formula

GUI (Ubuntu 14.04 and later): GParted v0.17 and later provide a nice GUI for this. (Older versions will refuse to resize a mounted partition).

Command line (any Ubuntu version): There are three steps to this.

Step 1. The partition must first be resized. If you're using LVM, it's easy, and you presumably know how to proceed. If you're using classic partitions, it's a bit more complicated, and may require a reboot (though you never have to boot another system or live CD).

This is how I do it: Use fdisk to first delete the partition (the idea is that the data on disk will be preserved), then carefully recreate it with a larger size at the same position.

Example:

$ sudo fdisk /dev/sda

Command (m for help): p

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     9437183     4717568   83  Linux

Command (m for help): d
Selected partition 1

Command (m for help): p

   Device Boot      Start         End      Blocks   Id  System

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4, default 1): 1
First sector (2048-10485759, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-10485759, default 10485759):
Using default value 10485759

Command (m for help): p

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1            2048    10485759     5241856   83  Linux

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.

Again, it is critical that the new partition starts at the same block as the old. The Id should also match (83 for Linux systems). Be prepared to lose all your data at the slightest typo.

To be on the safe side, you may also restore the boot flag (which according to Wikipedia is still required on some computers) by pressing a.

See the comment section for what to do if your swap partition is in the way.

By now it should be apparent why people recommend using a live CD. ;-)

Step 2. As fdisk helpfully reminds you, you must reload the partition table before proceeding. The safest way is to simply reboot; but you can also use partprobe or kpartx (more information).

Step 3. Once the partition is resized and the partition table reloaded, it's a simple matter of running resize2fs on the file system, and you can do this even when it's mounted as the root partition.

Example:

$ sudo resize2fs /dev/sda1

I will try to answer your questions in the order you asked them:

1. It depends on how Matlab and Mathematica are distributed; if they are distributed as static binaries, then you should be okay. A static binary has any of the libraries needed by the program compiled into them. Generally, this is not the default for compiled applications, as it leads to extremely large binaries.

2. There really aren't any disadvantages, per say; it depends on the application. If you're installing an application from apt-get, Synaptic or from the Ubuntu Software Centre, the application is being installed in your root partition. If you have a static binary that you have downloaded and unpackaged yourself, then your best bet would be to keep it in your home directory. For any scripts or programs I write or install, that are not provided by the Ubuntu repositories, I keep them in a bin directory in my home folder. This way, they aren't "polluting" my base system.

3. The size of your root partition really depends on how many applications and libraries you plan on installing from the Ubuntu repositories. Different Linux distributions recommend different sizes. If you allow Ubuntu to automatically partition your drive, with a separate partition for /home, the Ubuntu installer will give you a sane layout. C and C++ compilers, Lisp REPLs, Python interpreters and the various databases do not take up much room. The only large compiler is for Java; I believe it weighs in at around 80MB for the JDK (Java Development Kit). As with my answer for your second question, most of the stuff you write, you should keep to your home directory, so you do not pollute the base system. Plus, if you ever upgrade your Ubuntu install, you will not have to worry about accidentally blowing away the directory you keep your projects in. Granted, you run this risk anyways, it will just be easier to keep everything you do in your home directory; that is what it is there for.