5- Managed shared libraries and packages Management

Question 1

Any shared library file namw will have … in it

Answer 1

.so (shared object file which is a library)

Question 2

shared library locations

Answer 2

shared files between system and users

generally found in /lib/, usr/lib, /usr/lib64, /usr/local/lib

Question 3

static linking to shared libraries

Answer 3

Applications CONTAIN a full copy of the .so aka shared library file.
The contained library has all the characteristics expected by the application.
The library is that it is a fixed version and so doesn’t have the updates and fixes of later versions

Question 4

ldd

Answer 4

list of libraries that the application uses

ldd to know different libraries required
Ex : Which sshd –> ldd /usr/sbin/sshd

Question 5

ldconfig

Answer 5

Updates ld.so.cache file (located in /etc/)

creates the necessary links and cache to the most recent shared libraries found in the directories specified on the command line, in the file /etc/ld.so.conf, and in the trusted directories ( /lib/, usr/lib, /usr/lib64, /usr/local/lib)

Question 6

what’s /etc/ld.so.conf

Answer 6

It holds path settings which point to directories that hold (dynamic) libraries. It’s used by ldconfig to create necessary links and cache.
Programs, when dynamicaly compiled, need libraries to run. In general ld.so.conf holds the basic directories where these libs can be found. Sometimes you have to add another line to that file.

Question 7

aptitude vs synaptic

Answer 7

GUI based applications for Debian package management.

Question 8

where are the Debian package configuration files?

Answer 8

/etc/apt

Question 9

source.list

Answer 9

define the repositories that come with the system, which it means the repositories that will be installed during system installation.

Question 10

Two type of repositories are defined in source.list

Answer 10

deb repositories: which is a binary repository which will install libraries, application packages, ..etc
deb-src repository it contains the related source code for the packages that identified by deb repository

• Debian/ubuntu use a nick name (trusty used in 16.04 distribution) in url repository to pull information.
• restricted keyword it means a restricted software that it does not require license
• universe that software is not supported it means that it would not get software update.

Question 11

Command to update system app

Answer 11

apt-get update

• Any changes in repository configuration file required this command.
• This command updates all the repository to get a list of all the packages for each one of the URLs

Question 12

/etc/apt/source.list.d

Answer 12

directory in Ubuntu/Debian where third-party (non Ubuntu or Debian) repositories can be added

Question 13

How to add a new third-party repository for apt?

Answer 13

create a file in /etc/sources.list.d with the URL, and other qualifiers, then run apt-get update to refresh your local repo cache.

Question 14

apt-get upgrade

Answer 14

• must be used after apt-get update
• it updates the existing system and any installed software to the newest version that reported from the configuration repository for this distribution.
• to upgrade the system: apt-get dist-upgrade

Question 15

to remove app

Answer 15

apt-get remove app

- it does not remove config files that has been changed

Question 16

apt-get purge app

Answer 16

removes the packages and the configuration files

Question 17

a command to search for a package in a system

Answer 17

apt-cache search app

- This command will show any application that has similar name.

Question 18

a command to show information about specific package

How to get information about sshd?

Answer 18

apt-cache show app

apt-cache show sshd

Question 19

a command to show more technical information about thepackage

Answer 19

apt-cache showpkg app

- it show the required dependencies