101-500 Reviews Questions

The directories on a 64 bit Linux system that typically contain shared libraries are /usr/lib64/ and /lib64/. Shared libraries are binary files that provide reusable functions, routines, classes, data structures, and so on for programs and applications. They are loaded into memory before the program starts and shared by multiple processes that use the same library. Shared libraries are usually stored in standard locations in the file system, such as /usr/lib, /usr/local/lib, /lib, and /lib64 for 32 bit systems, and /usr/lib64, /usr/local/lib64, /lib64, and /lib for 64 bit systems12. The /usr/lib64 and /lib64 directories contain the shared libraries for the system and user applications, respectively. The other directories are either non-existent or do not contain shared libraries. The ~/.lib64/ directory is not a standard location for shared libraries, and it is unlikely that a user would have such a directory in their home directory. The /var/lib64/ directory is also not a standard location for shared libraries, and it is usually used for variable data files that are specific to a package or application. The /opt/lib64/ directory is not a standard location for shared libraries, and it is usually used for optional software packages that are installed in the /opt directory3. References:

• Linux Essentials - Linux Professional Institute Certification Programs1
• Exam 101 Objectives - Linux Professional Institute2
• Understanding Shared Libraries in Linux - Tecmint3

 The action that ensures that a faulty kernel module is not loaded automatically when the system boots is adding a blacklist line including the name of the offending module to the file /etc/modprobe.d/blacklist.conf. This file contains a list of kernel modules that are prevented from loading by the modprobe command, which is used to load and unload modules from the running kernel. By adding a line like blacklist  to this file, the module will be ignored by modprobe unless it is explicitly specified as aparameter. This way, the module will not be loaded at boot time or by other modules that depend on it. The other options are either invalid or do not affect the automatic loading of the module. Using lsmod --remove --autoclean without specifying the name of a specific module will not work, because lsmod does not have such options and it is only used to display the currently loaded modules. Using modinfo –k followed by the name of the offending module will not work, because modinfo does not have a -k option and it is only used to display information about a module. Using modprobe –r followed by the name of the offending module will only remove the module from the running kernel, but it will not prevent it from loading again at the next boot. Deleting the kernel module’s directory from the file system and recompiling the kernel, including its modules, is a drastic and unnecessary measure that will not only remove the faulty module, but also all other modules in that directory, and it will require a lot of time and expertise to perform. References:

• Linux Essentials - Linux Professional Institute Certification Programs1
• Exam 101 Objectives - Linux Professional Institute2
• Linux Kernel Module Management 101 - Linux.com1
• Chapter 2. Managing kernel modules - Red Hat Customer Portal2

 The jobs command displays a list of all background tasks running in the current shell. A background task is a process that is started with the & operator or suspended with Ctrl+Z and resumed with the bg command. The jobs command shows the job number, the status, and the command name of each background task. For example, the following output shows two background tasks: one is running (sleep 10) and one is stopped (ping

1- Running sleep 10 & 2+ Stopped ping

References:

• [LPI Exam 101 Detailed Objectives], Topic 103: GNU and Unix Commands, Objective 103.5: Create, monitor and kill processes, Weight: 4, Key Knowledge Areas: Use of jobs, fg and bg commands.
• How to Run and Control Background Processes on Linux, Topic: The jobs Command.

The problem with the command

sed -e “s/a/b/” /tmp/file >/tmp/file

is that it tries to read and write from the same file, which results in overwriting the file before the command can process it. The shell sets up the redirection by opening the file /tmp/file for writing and truncating it to zero length. Then it executes the sed command, which tries to read from the same file, but finds it empty. Therefore, the output is also empty and the file remains empty. A possible solution is to use a temporary file for the output and then rename it to the original file name. For example:

sed -e “s/a/b/” /tmp/file >/tmp/file.tmp && mv /tmp/file.tmp /tmp/file

This way, the original file is not overwritten until the sed command finishes successfully. The other options are either incorrect or not applicable. The file order is correct, the sed command does match something in the file, and the > character is valid for redirection. The | character is used for piping, not redirection. References:

• LPIC-1 Exam 101 Objectives, Topic 103: GNU and Unix Commands, 103.4 Use streams, pipes and redirects
• LPIC-1 Linux Administrator 101-500 Exam FAQ, LPIC-1 Exam 101 Objectives, GNU and Unix Commands (Total Weight: 25)