3. Linux installation and package management

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Linux Hard Disk Layout

/usr - user binaries are stored when packages are installed.

/home - user's home directory lives where user can store their own files.

/boot - where the boot loader and all the images required for booting live.

/var - where all the variable data like log, etc. lives

/tmp - unique storage area where anyone can write to.

Partitions

Divide storage into multiple pieces

Allows dual booting

separation of files. System on one paritions and backup on some other partition

Data organization. Keeping work and home files in different places

System protection with partitions

create partitions

moount them to directories

We can mount to:

.home

/var

/tmp

/home/nick/blah

You can even mount a partition over a directory already consisting of some files. So, after mounting, the previous existing files of that directory will be hidden and only the ones corresponding to the partition being mounted will be there.

When you un-mount the partition from that directory, the previous files will be back.

Swap partition

This is used when the physical memory or RAM is full. When system needs more memory, then inactive pages in your memory are moved to swap partition to free up more memory to work with.

LVM

Logical volume manager

split disks into pools

create partitions from pools

can grow or shrink partitions

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Install a boot manager

Boot loader

Boots a linux system

Runs before the operating system

can be configured from the operating system

Common boot loaders - LILO (Linux Loader), GRUB Legacy, GRUB 2

grub probe - lets you probe device information for grub

grub probe --version - provides the version of grub

grub install --version - produces the same output

cd /boot

ls

we can see a few linux kernels, few config files, initrd images and the grub directory here

So,

cd /grub

ls

our main configuration file here is grub.cfg. This can vary from system to system.

So, in grub legacy, it was "menu.lst" and it has also been known as grub.conf"

However most systems have standardized to use grub.cfg

less.cfg

You locate in this file, the code responsible for differnet options like advanced options for linux.

cd /etc/grub.d

ls

these are the scripts used to generate grub.cfg

Now, to deal with the default configuration/options pf GRUB,

edit the /etc/default/grub file

So, update this file accordingly and run the command update-grub

Now, to know what exactly update-grub does, firstly let's find where does the binary for the update-grub command lie

enter

which update-grub

This will output the path to update-grub

then, execute the following command to check out the script behind update-grub

cat /usr/bin/update-grub

Now, reboot and you will see the update

There is one more thing you can do directly from GRUB. So, change the default target/run level directly from grub.

So, when grub is open, enter "e" to enter commnd line mode.

There will open up a script.

Now, go to the line near the bottom starting with "linux" and at the end of that line, enter this

systemd.unit=rescue.target

This would set the default target to rescue target.

Then, press F10 to boot and you'll be booted, as expected, into rescue mode.

Rescue mode is useful if you system fails to load due to some reason. In rescue mode, some basic services are loaded and then, you are just given terminal access. So, then you can login as root and repair your system with command line.

fter the required reparation, you can execute the reboot command or press Ctrl-D to straight away reboot to normal mode.

Had grub not been installed for you and you had the grub config file ready, we would have to install grub to master boot record. So, for that, execute this,

grub install /dev/sda (/dev/sda is your harddisk where grub will be installed)