What is directory services in linux

Linux Directory Structure and Important Files Paths Explained

For any person, who does not have a sound knowledge of Linux Operating System and Linux File System, dealing with the files and their location, their use may be horrible, and a newbie may really mess up.

This article is aimed to provide the information about Linux File System, some of the important files, their usability and location.

Linux Directory Structure Diagram

A standard Linux distribution follows the directory structure as provided below with Diagram and explanation.

Linux Directory Structure

Each of the above directory (which is a file, at the first place) contains important information, required for booting to device drivers, configuration files, etc. Describing briefly the purpose of each directory, we are starting hierarchically.

1. /bin : All the executable binary programs (file) required during booting, repairing, files required to run into single-user-mode, and other important, basic commands viz., cat, du, df, tar, rpm, wc,history, etc.
2. /boot : Holds important files during boot-up process, including Linux Kernel.
3. /dev : Contains device files for all the hardware devices on the machine e.g., cdrom, cpu, etc
4. /etc : Contains Application’s configuration files, startup, shutdown, start, stop script for every individual program.
5. /home : Home directory of the users. Every time a new user is created, a directory in the name of user is created within home directory which contains other directories like Desktop, Downloads, Documents, etc.
6. /lib : The Lib directory contains kernel modules and shared library images required to boot the system and run commands in root file system.
7. /lost+found : This Directory is installed during installation of Linux, useful for recovering files which may be broken due to unexpected shut-down.
8. /media : Temporary mount directory is created for removable devices viz., media/cdrom.
9. /mnt : Temporary mount directory for mounting file system.
10. /opt : Optional is abbreviated as opt. Contains third party application software. Viz., Java, etc.
11. /proc : A virtual and pseudo file-system which contains information about running process with a particular Process-id aka pid.
12. /root : This is the home directory of root user and should never be confused with ‘/‘
13. /run : This directory is the only clean solution for early-runtime-dir problem.
14. /sbin : Contains binary executable programs, required by System Administrator, for Maintenance. Viz., iptables, fdisk, ifconfig, swapon, reboot, etc.
15. /srv : Service is abbreviated as ‘srv‘. This directory contains server specific and service related files.
16. /sys : Modern Linux distributions include a /sys directory as a virtual filesystem, which stores and allows modification of the devices connected to the system.
17. /tmp :System’s Temporary Directory, Accessible by users and root. Stores temporary files for user and system, till next boot.
18. /usr : Contains executable binaries, documentation, source code, libraries for second level program.
19. /var : Stands for variable. The contents of this file is expected to grow. This directory contains log, lock, spool, mail and temp files.

Exploring Important file, their location and their Usability

Linux is a complex system which requires a more complex and efficient way to start, stop, maintain and reboot a system unlike Windows. There is a well defined configuration files, binaries, man pages, info files, etc. for every process in Linux.

1. /boot/vmlinuz : The Linux Kernel file.
2. /dev/hda : Device file for the first IDE HDD (Hard Disk Drive)
3. /dev/hdc : Device file for the IDE Cdrom, commonly
4. /dev/null : A pseudo device, that don’t exist. Sometime garbage output is redirected to /dev/null, so that it gets lost, forever.
5. /etc/bashrc : Contains system defaults and aliases used by bash shell.
6. /etc/crontab : A shell script to run specified commands on a predefined time Interval.
7. /etc/exports : Information of the file system available on network.
8. /etc/fstab : Information of Disk Drive and their mount point.
9. /etc/group : Information of Security Group.
10. /etc/grub.conf : grub bootloader configuration file.
11. /etc/init.d : Service startup Script.
12. /etc/lilo.conf : lilo bootloader configuration file.
13. /etc/hosts : Information of Ip addresses and corresponding host names.
14. /etc/hosts.allow : List of hosts allowed to access services on the local machine.
15. /etc/host.deny : List of hosts denied to access services on the local machine.
16. /etc/inittab : INIT process and their interaction at various run level.
17. /etc/issue : Allows to edit the pre-login message.
18. /etc/modules.conf : Configuration files for system modules.
19. /etc/motd : motd stands for Message Of The Day, The Message users gets upon login.
20. /etc/mtab : Currently mounted blocks information.
21. /etc/passwd : Contains password of system users in a shadow file, a security implementation.
22. /etc/printcap : Printer Information
23. /etc/profile : Bash shell defaults
24. /etc/profile.d : Application script, executed after login.
25. /etc/rc.d : Information about run level specific script.
26. /etc/rc.d/init.d : Run Level Initialisation Script.
27. /etc/resolv.conf : Domain Name Servers (DNS) being used by System.
28. /etc/securetty : Terminal List, where root login is possible.
29. /etc/skel : Script that populates new user home directory.
30. /etc/termcap : An ASCII file that defines the behaviour of Terminal, console and printers.
31. /etc/X11 : Configuration files of X-window System.
32. /usr/bin : Normal user executable commands.
33. /usr/bin/X11 : Binaries of X windows System.
34. /usr/include : Contains include files used by ‘c‘ program.
35. /usr/share : Shared directories of man files, info files, etc.
36. /usr/lib : Library files which are required during program compilation.
37. /usr/sbin : Commands for Super User, for System Administration.
38. /proc/cpuinfo : CPU Information
39. /proc/filesystems : File-system Information being used currently.
40. /proc/interrupts : Information about the current interrupts being utilised currently.
41. /proc/ioports : Contains all the Input/Output addresses used by devices on the server.
42. /proc/meminfo : Memory Usages Information.
43. /proc/modules : Currently using kernel module.
44. /proc/mount : Mounted File-system Information.
45. /proc/stat : Detailed Statistics of the current System.
46. /proc/swaps : Swap File Information.
47. /version : Linux Version Information.
48. /var/log/lastlog : log of last boot process.
49. /var/log/messages : log of messages produced by syslog daemon at boot.
50. /var/log/wtmp : list login time and duration of each user on the system currently.

That’s all for now. Keep connected to Tecmint for any News and post related to Linux and Foss world. Stay healthy and Don’t forget to give your value-able comments in comment section.

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What Is /etc/services in Linux/Unix?

The Linux Services files store well-known ports

UNIX operating systems store what’s called a services file at /etc/services. It stores information about numerous services that client applications might use on the computer. Within the file are the service name, port number, and protocol it uses, and any applicable aliases.

The port numbers are mapped to specific services just like the host’s file on Windows computers map a hostname to an IP address. However, the UNIX operating system’s services file does not include IP addresses but instead information like whether the service is TCP or UDP and what common names it might go by.

Example of a UNIX Services File

On UNIX, the key role of the configuration file /etc/services is so that programs can do a getportbyname() sockets call in their code in order to understand what port they should use. For example, a POP3 email daemon queries getportbyname (POP3) to retrieve the number 110 that POP3 runs on.

The idea is that if all POP3 daemons use getportbyname(), then no matter what POP3 daemon you run, you can always reconfigure its port number by editing /etc/services.

It’s unreliable to use the services file to discern what port numbers mean. To find out what ports programs are using, you should instead use the program lsof to find out exactly which ports are bound to which processes. If running lsof is not appropriate, then you should research the ports in a more generic reference.

Syntax

All services files follow the same syntax of:

However, an alias and comment for each database entry are not necessary, as you can see in this example services file:

The Unix operating system is a family of operating systems. Android, macOS, and Linux are all Unix variants. Unix builds robust, multi-user environments that are good for desktops and servers.

Use the Unix/Linux mv command via a Terminal window to move files and folders around your computer. Alternatively, your Unix/Linux distribution should come with a file manager. Commonly used file managers include Nautilus, Dolphin, Thunar, PCManFM, and Caja.

A Unix shell is a Unix system interface that acts as a command-line interpreter. The Unix shell receives your input via the keyboard and then sends those commands and programs to the operating system to execute.

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Linux Unix *nix

What Is – Directory Services

What is a Directory service– (According to Wikipedia) “A directory service is the software system that stores, organizes and provides access to information in a directory. In software engineering, a directory is a map between names and values. It allows the lookup of values given a name, similar to a dictionary. As a word in a dictionary may have multiple definitions, in a directory, a name may be associated with multiple, different pieces of information. Likewise, as a word may have different parts of speech and different definitions, a name in a directory may have many different types of data.”

There have been numerous forms of directory service implementations from different vendors.

• DNS
• NIS and NIS+ (Sun Microsystem’s implemetation of a directory service)
• OpenLDAP (Open Source Ldap protocol based implementation)
• Active Directory (Microsoft’s implementation of Ldap protocol)
• And many more…..

LDAP– (Lightweight Directory Access Protocol) is a protocol for accessing directory services in order to retrieve data. It is a lightweight client-server protocol. The information in a directory is read more often than it is written. It is on the application layer of the TCP/IP protocol suite.

Important Files for directory service:-
/etc/nsswitch.conf = The name service switch config file. This is a very important file and is found on most flavours of Unix. This file mentions the currently running name service in your environment. The name services can be NIS, NIS+, LDAP and more.

LDAP daemons which should be running on a client machine:-
1) sssd (stands for System Security Services daemon)
is a service which provides access to different identity and authentication providers. You can configure SSSD to use a native LDAP domain (that is, an LDAP identity provider with LDAP authentication), or an LDAP identity provider with Kerberos authentication.
2) nslcd (stands for local LDAP name service daemon)
nslcd is a daemon that will do LDAP queries for local processes based on a simple configuration file.
3) oddjobd

To configure LDAP
On RHEL and CentOS (I have not checked on other flavours) if you run #system-config-authentication
the “Authentication Configuration” window opens and you can edit the settings according to your requirements.

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