Linux Certification

The chown command changes the owner of the file or directory specified by the File or Directory parameter to the user specified by the Owner parameter.  In this command syntax, if only a user name (or numeric user ID) is given, that user is made the owner of each given file, and the file’s group is not changed and if the user name is followed by a colon and a group name (or numeric group ID), with no spaces between them, the group ownership of the files is changed as well.  Command flags of chown command are as follows:

The newgrp command changes temporarily the primary group of a user into another group of which that user is a member. In this step, a new shell will be created, and when that user will exit from the shell, his previous group will be reinstated. If no group is specified, the GID is changed to the login GID. The newgrp command does not take input from standard input and cannot be run from within a script.

The repquota command is prints a summary of quotas and disk usage for a file system specified by the filesystem parameter.  Important flags of repquota commands are as follows:

-a Specifies that quotas are printed for all file systems enabled with quotas in the /etc/filesystems file.
-c Changes the output of the command to a colon-delineated format.
-g Specifies that only group quotas are printed.
-l Enables long user names to be printed on the repquota report.
-u Specifies that only user quotas are printed.
-v Prints a header line before the summary of quotas for each file system

The edquota command extracts the quota information for a user from the various filesystems with quotas enabled. The edquota command creates a temporary file that contains current disk quotas of each user and group. It determines the list of file systems with established quotas from the /etc/filesystems file.

The edquota command also invokes the vi editor (or the editor specified by the EDITOR environment variable) on the temporary file so that quotas can be added and modified. It creates a temporary file and opens an editor for the user to adjust the quotas. The list of filesystems with user quotas is determined by scanning the mounted filesystems for a .quota.ops.user file located at its root.

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The /proc file system is responsible to control access to physical devices on the computer and to schedule when and how processes interact with these devices. The /proc/ directory contains a hierarchy of special files which represent the current state of the kernel — allowing applications and users to peer into the kernel’s view of the system.Many of the entries in /proc provide access to information about the running kernel’s configuration and state. Some of these entries are at the top level of /proc; others are under /proc/sys/kernel.

Version Information
The file /proc/version contains a long string describing the kernel’s release number and build version. It also includes information about how the kernel was built: the user who compiled it, the machine on which it was compiled, the date it was compiled, and the compiler release that was used, for example:

The setserial command is used to set and report the configuration information associated with a serial port. This information includes which I/O port and IRQ are being used by a particular serial port.  Often  setserial command is called from an rc.serial script, which is usually run out of /etc/rc.local.

The options in the setserial command is as follows:

The locate command is used to locate files in the whole system using a database of filenames.
Syntax: locate <filename>

It searches the locate database for the filename. This database is stored  in  /var/lib/locatedb.It is updated via the following command:

updatedb [options]

 
The configuration file for updatedb is /etc/updatedb.conf.

Options of the updatedb command:

 
-d path, –database=path: Instead of searching the default file name database, search the file namedatabases in path, which is a colon-separated list of database file names. You can also use the environment variable LOCATE_PATH to set the list of database files to search. The option overrides the environment variable if both are used.

Traceroute is a command which can show you the path a packet of information takes from your computer to one you specify. It will list all the routers it passes through until it reaches its destination, or fails to and is discarded. Traceroute works by increasing the “time-to-live” value of each successive batch of packets sent. The first three packets sent have a time-to-live (TTL) value of one (implying that they are not forwarded by the next router and make only a single hop). The next three packets have a TTL value of 2, and so on. When a packet passes through a host, normally the host decrements the TTL value by one, and forwards the packet to the next host. When a packet with a TTL of one reaches a host, the host discards the packet and sends an ICMP time exceeded (type 11) packet to the sender. The traceroute utility uses these returning packets to produce a list of hosts that the packets have transverse in route to the destination.

What is LDAP schema: Similar types of object-classes and attributes are grouped together in a packaging unit, known as LDAP schema. In LDAP directories, schemas are added using the include statements in the slapd.conf (configuration file). An LDAP schema must contain at least one object class. An attribute added to one schema can also be used by an object class of another schema. A schema that represents individual people within organizations is known as a white pages schema.

What does LDAP schema store: The contents of the entries in a sub-tree are governed by a schema. For continue reading, please visit LDAP Schema