In Windows we have DLLs (Dynamic Linked Libraries), in Linux we have libLIBNAME.so.VERSION files. Ex - libcurl.so.1.5.2.
Storage directories: /lib, /lib64, /usr/lib, or /usr/lib64.
ldd: shows if a program is statically or dynamically linked, also lists all libraries that are linked to the program (if dynamic).
We often have one library pointing to another like libudev.so.1 -> libudev.so.1.4.0. So if a software uses the former, it will implicitly use the latter.
We can use ls -l to check symbolic links.
$ ls -la /lib/i386-linux-gnu/libudev.so.1
lrwxrwxrwx 1 root root 16 Nov 13 23:05 /lib/i386-linux-gnu/libudev.so.1 -> libudev.so.1.4.0
$ cat /etc/ld.so.conf
include ld.so.conf.d/*.conf
$ ls /etc/ld.so.conf.d/
llvm13-x86_64.conf pipewire-jack-x86_64.conf
$ cat /etc/ld.so.conf.d/llvm13-x86_64.conf
/usr/lib64/llvm13/lib
How to locate the libs?: It is a common strategy to place libraries' paths in /etc/ld.so.conf.d/*.conf files, and a single config file /etc/ld.so.conf can include all those single .conf files.
Also, there exists a ld.so.cache file in /etc that contains symbolic links to all dynamically linked libraries on the system, so that we don’t have to traverse ld.so.config.d everytime.
Every software on the system reads this cache file to look for libraries. We use ldconfig command to manage this cache file.
ldconfig -p
# after editing the config file, run the command again to update the cache
ldconfig
When a software needs a library, it looks it up in the following order:
etc/ld.so.conf (which might load other libraries from /etc/ld.so.conf.d)/lib, /lib64, /usr/lib, and /usr/lib64Package: pre-compiled software
Package management systems exist to download, update, remove packages with CLI
Repository: Each distro has a pre-configured set of repositories from where it downloads the packages
In Debian based systems, packages are named as NAME-VERSION-RELEASE_ARCHITECTURE.deb and the sources list is stored in /etc/apt/sources.list file and /etc/apt/sources.list.d/ directory.
Advanced Package Tool (APT)
apt-get update # updates sources list only, no packages are updated
apt-get upgrade # upgrade all installed packages
apt-get install package_1 package_2 package_3 # install; upgrade if already installed
apt-get install package_name=VERSION_NUMBER # install specific version
apt-get remove pkg_name # removing a package will not remove its dependencies and config files! (since it can be a shared dependency that maybe used by other programs) (also configs remain on the system)
apt-get purge pkg_name # remove a package and its config files
apt-get autoremove pkg_name # remove unused dependencies of this package (dependencies that only this package used and no other package on the system uses) (doesn't remove config files)
apt-get autoremove # remove all unused dependencies globally (for all packages)
apt search search_string # search a package
apt show package # get info about a package
The Debian Package Management System (dpkg) is used to perform low-level actions on .deb packages. Show config, display status, show info, reconfigure, etc…
apt uses dpkg under the hood. Once apt downloads .deb package files, dpkg is used to perform actions on them.
Debian based distros: apt, dpkg, aptitude
Red-Hat based: RPM (Red Hat Package Manager), YUM (Yellowdog Updater, Modified), DNF (Dandified Yum)
Arch based: Pacman
Often times the programs in linux have a .tar.gz extension.
gzip is a tool that can compress a single file at a time.
tar is a tool that can create a archive containing multiple files.
If we combine those, we get a compressed tarball (.tar.gz). In order to extract the contents, we do the reverse, first unzip and then unpack.