How VPS - How to use/setup VPS
  • Home
  • Management guides
    • Web servers software
      • Directadmin
      • Hocvps Script
      • Centmin Mod
      • CWP
      • Kloxo-MR
      • Plesk
    • Control Panels
    • Securing VPS/Servers
      • SSL Certificates
      • Upgrading
      • Authentication
  • Operating System
    • CentOS
    • Fedora
    • Debian
    • Linux
    • Arch
    • BSD
    • CoreOS
  • Reviews
  • Coupon
    • Domain Coupon
    • Hosting Coupon
No Result
View All Result
  • Home
  • Management guides
    • Web servers software
      • Directadmin
      • Hocvps Script
      • Centmin Mod
      • CWP
      • Kloxo-MR
      • Plesk
    • Control Panels
    • Securing VPS/Servers
      • SSL Certificates
      • Upgrading
      • Authentication
  • Operating System
    • CentOS
    • Fedora
    • Debian
    • Linux
    • Arch
    • BSD
    • CoreOS
  • Reviews
  • Coupon
    • Domain Coupon
    • Hosting Coupon
No Result
View All Result
How VPS - How to use/setup VPS
No Result
View All Result
Home Operating System Linux

Understanding Shared Libraries in Linux

How VPS by How VPS
November 2, 2018
in Linux, Operating System
0
0
SHARES
53
VIEWS
Share on FacebookShare on Twitter

Contents

  1. Shared Library Naming Conventions
  2. Locating Shared Libraries in Linux
  3. Managing Shared Libraries in Linux
    1. Sample Output

In programming, a library is an assortment of pre-compiled pieces of code that can be reused in a program. Libraries simplify life for programmers, in that they provide reusable functions, routines, classes, data structures and so on (written by a another programmer), which they can use in their programs.

For instance, if you are building an application that needs to perform math operations, you don’t have to create a new math function for that, you can simply use existing functions in libraries for that programming language.

Examples of libraries in Linux include libc (the standard C library) or glibc (GNU version of the standard C library), libcurl (multiprotocol file transfer library), libcrypt (library used for encryption, hashing, and encoding in C) and many more.

Linux supports two classes of libraries, namely:

  • Static libraries – are bound to a program statically at compile time.
  • Dynamic or shared libraries – are loaded when a program is launched and loaded into memory and binding occurs at run time.

Dynamic or shared libraries can further be categorized into:

  • Dynamically linked libraries – here a program is linked with the shared library and the kernel loads the library (in case it’s not in memory) upon execution.
  • Dynamically loaded libraries – the program takes full control by calling functions with the library.

Shared Library Naming Conventions

Shared libraries are named in two ways: the library name (a.k.a soname) and a “filename” (absolute path to file which stores library code).

For example, the soname for libc is libc.so.6: where lib is the prefix, c is a descriptive name, so means shared object, and 6 is the version. And its filename is: /lib64/libc.so.6. Note that the soname is actually a symbolic link to the filename.

Locating Shared Libraries in Linux

Shared libraries are loaded by ld.so (or ld.so.x) and ld-linux.so (or ld-linux.so.x) programs, where x is the version. In Linux, /lib/ld-linux.so.x searches and loads all shared libraries used by a program.

A program can call a library using its library name or filename, and a library path stores directories where libraries can be found in the filesystem. By default, libraries are located in /usr/local/lib, /usr/local/lib64, /usr/lib and /usr/lib64; system startup libraries are in /lib and /lib64. Programmers can, however, install libraries in custom locations.

The library path can be defined in /etc/ld.so.conf file which you can edit with a command line editor.

# vi /etc/ld.so.conf 

The line(s) in this file instruct the kernel to load file in /etc/ld.so.conf.d. This way, package maintainers or programmers can add their custom library directories to the search list.

If you look into the /etc/ld.so.conf.d directory, you’ll see .conf files for some common packages (kernel, mysql and postgresql in this case):

# ls /etc/ld.so.conf.d

kernel-2.6.32-358.18.1.el6.x86_64.conf  kernel-2.6.32-696.1.1.el6.x86_64.conf  mariadb-x86_64.conf
kernel-2.6.32-642.6.2.el6.x86_64.conf   kernel-2.6.32-696.6.3.el6.x86_64.conf  postgresql-pgdg-libs.conf

If you take a look at the mariadb-x86_64.conf, you will see an absolute path to package’s libraries.

# cat mariadb-x86_64.conf

/usr/lib64/mysql

The method above sets the library path permanently. To set it temporarily, use the LD_LIBRARY_PATH environment variable on the command line. If you want to keep the changes permanent, then add this line in the shell initialization file /etc/profile (global) or ~/.profile (user specific).

# export LD_LIBRARY_PATH=/path/to/library/file

Managing Shared Libraries in Linux

Let us now look at how to deal with shared libraries. To get a list of all shared library dependencies for a binary file, you can use the ldd utility. The output of ldd is in the form:

library name =>  filename (some hexadecimal value)
OR
filename (some hexadecimal value)  #this is shown when library name can’t be read

This command shows all shared library dependencies for the ls command.

# ldd /usr/bin/ls
OR
# ldd /bin/ls
Sample Output
	linux-vdso.so.1 =>  (0x00007ffebf9c2000)
	libselinux.so.1 => /lib64/libselinux.so.1 (0x0000003b71e00000)
	librt.so.1 => /lib64/librt.so.1 (0x0000003b71600000)
	libcap.so.2 => /lib64/libcap.so.2 (0x0000003b76a00000)
	libacl.so.1 => /lib64/libacl.so.1 (0x0000003b75e00000)
	libc.so.6 => /lib64/libc.so.6 (0x0000003b70600000)
	libdl.so.2 => /lib64/libdl.so.2 (0x0000003b70a00000)
	/lib64/ld-linux-x86-64.so.2 (0x0000561abfc09000)
	libpthread.so.0 => /lib64/libpthread.so.0 (0x0000003b70e00000)
	libattr.so.1 => /lib64/libattr.so.1 (0x0000003b75600000)

Because shared libraries can exist in many different directories, searching through all of these directories when a program is launched would be greatly inefficient: which is one of the likely disadvantages of dynamic libraries. Therefore a mechanism of caching employed, performed by a the program ldconfig.

By default, ldconfig reads the content of /etc/ld.so.conf, creates the appropriate symbolic links in the dynamic link directories, and then writes a cache to /etc/ld.so.cache which is then easily used by other programs.

This is very important especially when you have just installed new shared libraries or created your own, or created new library directories. You need to run ldconfig command to effect the changes.

# ldconfig
OR
# ldconfig -v 	#shows files and directories it works with

After creating your shared library, you need to install it. You can either move it into any of the standard directories mentioned above, and run the ldconfig command.

Alternatively, run the following command to create symbolic links from the soname to the filename:

# ldconfig -n /path/to/your/shared/libraries

To get started with creating your own libraries, check out this guide from The Linux Documentation Project(TLDP).

Thats all for now! In this article, we gave you an introduction to libraries, explained shared libraries and how to manage them in Linux. If you have any queries or additional ideas to share, use the comment form below.

Source: tecmint.com

Tags: Linux Commandslinux guidelinux vps setup guide
How VPS

How VPS

Related Posts

Failed to download metadata for repo 'appstream' on Centos 8
CentOS

How to fix error: Failed to download metadata for repo ‘appstream’ on Centos 8

February 25, 2022
How to Install Apache Tomcat 8 on CentOS 7
Linux

How to Install Apache Tomcat 8 on CentOS 7?

February 11, 2020
Install Arch Linux With Btrfs Snapshotting
Uncategorized

Install Arch Linux With Btrfs Snapshotting

February 13, 2020
Next Post
Comparison of Shared Hosting, VPS, Dedicated Servers, and Cloud Servers

Comparison of Shared Hosting, VPS, Dedicated Servers, and Cloud Servers

Pydf an Alternative “df” Command to Check Disk Usage in Different Colours

Learn How to Use ‘dir’ Command with Different Options and Arguments in Linux

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Follow Us

  • 121 Followers
  • 87.2k Followers

Recommended

Cloudwith.me Review

4 years ago

How to Use ‘find’ Command to Search for Multiple Filenames (Extensions) in Linux

4 years ago

13 Linux Network Configuration and Troubleshooting Commands

4 years ago

How to Deploy Ghost v0.11 LTS on Ubuntu 16.04

3 years ago

Instagram

    Please install/update and activate JNews Instagram plugin.

Categories

  • Arch
  • Authentication
  • Backups
  • BSD
  • Centmin Mod
  • CentOS
  • Control Panels
  • CoreOS
  • CWP
  • Debian
  • Directadmin
  • Encryption
  • Fedora
  • Firewalls
  • Hocvps Script
  • Hosting providers
  • Kloxo-MR
  • Linux
  • Mitigations
  • Operating System
  • Plesk
  • Reviews
  • Securing VPS/Servers
  • Security Patches
  • SSL Certificates
  • Uncategorized
  • Upgrading
  • VPS/Servers management guides
  • Vulnerability Detection
  • Web servers software
  • Webhosting Control Panel

Topics

Apache Web Server Bluehost Review 2019 Bluehost Review 2020 Bluehost Review 2021 Centmin Mod CentminMod centos install htop fsck htop install HTTP DoS attack Install Snort on an Ubuntu install Zabbix on CentOS install Zabbix on CentOS 7 Linux Commands linux guide linux install htop linux vps setup guide MariaDB MariaDB Error Mysql mysqld error optimize MariaDB optimize Mysql snort Ubuntu
No Result
View All Result

Highlights

Top Free Web Hosting Control Panels To Manage VPS/Dedicated Servers

Webmin Reviews

Virtualmin Reviews

CentOS Web Panel Reviews

Ajenti Reviews

ISPConfig Reviews

Trending

Failed to download metadata for repo 'appstream' on Centos 8
CentOS

How to fix error: Failed to download metadata for repo ‘appstream’ on Centos 8

by How VPS
February 25, 2022
0

I tried to update some extensions by use yum on centOs which I specified in Dockerfile. After...

How to Fix MySQL Error "Plugin 'InnoDB' registration as a STORAGE ENGINE failed"?

How to Fix MySQL Error “Plugin ‘InnoDB’ registration as a STORAGE ENGINE failed”?

November 17, 2020
How to optimize Mysql or MariaDB

How to optimize Mysql or MariaDB

November 3, 2020
Top Free Web Hosting Control Panels To Manage VPS/Dedicated Servers

Top Free Web Hosting Control Panels To Manage VPS/Dedicated Servers

February 17, 2020
Webmin Reviews

Webmin Reviews

February 17, 2020
How VPS – How to use/setup VPS

We bring you the best Premium WordPress Themes that perfect for news, magazine, personal blog, etc. Visit our landing page to see all features & demos.
LEARN MORE »

Recent News

  • How to fix error: Failed to download metadata for repo ‘appstream’ on Centos 8 February 25, 2022
  • How to Fix MySQL Error “Plugin ‘InnoDB’ registration as a STORAGE ENGINE failed”? November 17, 2020
  • How to optimize Mysql or MariaDB November 3, 2020

Categories

  • Arch
  • Authentication
  • Backups
  • BSD
  • Centmin Mod
  • CentOS
  • Control Panels
  • CoreOS
  • CWP
  • Debian
  • Directadmin
  • Encryption
  • Fedora
  • Firewalls
  • Hocvps Script
  • Hosting providers
  • Kloxo-MR
  • Linux
  • Mitigations
  • Operating System
  • Plesk
  • Reviews
  • Securing VPS/Servers
  • Security Patches
  • SSL Certificates
  • Uncategorized
  • Upgrading
  • VPS/Servers management guides
  • Vulnerability Detection
  • Web servers software
  • Webhosting Control Panel

[mc4wp_form]

© 2018 JNews - City News Magazine WordPress theme. All rights belong to their respective owners.
JNews is a top selling 2018 WordPress News, Blog, Newspaper & Magazine Theme.

No Result
View All Result
  • Home

© 2023 JNews - Premium WordPress news & magazine theme by Jegtheme.