LPI 101-500 Dumps

The tr command is used to translate, squeeze, or delete characters from a file or a stream. The -d option is used to delete characters that appear in the first operand. The \r and \n are escape sequences that represent the carriage return and the line feed characters, respectively. The CR-LF pair is the standard line ending for Windows text files, while the LF character is the standard line ending for Linux text files. Therefore, the command tr –d ‘\r’ < userlist.txt > newlist.txt will delete all the CR characters from the userlist.txt file and redirect the output to the newlist.txt file, effectively converting the line endings from Windows to Linux format. The other commands are incorrect because they either use the wrong syntax, the wrong operands, or the wrong redirection. References:

• LPI 101-500 Exam Objectives, Topic 103.7, Weight 4
• LPI Learning Materials, Chapter 3.7, Basic Scripting
• Web Search Results, 1

QUESTIONNO: 54

When in Normal mode invi, which character can be used to begin a reverse search of the text?

A.?

B./

C.F

D.r

Answer: A

 In vi, the ? character can be used to begin a reverse search of the text. This means that the search will start from the current cursor position and move backwards towards the beginning of the file. The search pattern can be any regular expression that matches the desired text. To repeat the search, the user can press n for the previous match or N for the next match. The / character can be used to begin a forward search of the text, which means that the search will start from the current cursor position and move forwards towards the end of the file. The F and r characters are not used for searching, but for other commands in vi. The F command is used to move the cursor to a previous occurrence of a specified character in the current line. The r command is used to replace the character under the cursor with another character. References:

• LPI 101-500 Exam Objectives, Topic 103.8, Weight 4
• LPI Learning Materials, Chapter 3.8, Advanced Scripting
• Web Search Results, 

The correct commands to create an ext3 filesystem on /dev/sdb1 are /sbin/mke2fs -j /dev/sdb1 and /sbin/mkfs -t ext3 /dev/sdb1. These commands format the partition /dev/sdb1 with the ext3 filesystem type. The first command uses the mke2fs utility with the -j option, which enables journaling. The second command uses the mkfs utility with the -t option, which specifies the filesystem type. Both commands are equivalent and can be used interchangeably. The other options are incorrect because they use the wrong syntax or parameters for the commands. Option C is wrong because the -c option for the mkfs command checks the device for bad blocks, not the filesystem type. Option D is wrong because there is no such utility as mke3fs. The correct utility name is mke2fs.

The correct command to enable the setuid (suid) permission on the executable /bin/foo is:

B. chmod 4755 /bin/foo

The chmod command is used to change the permissions of files and directories in Linux. The chmod command can take either a symbolic or a numeric mode to specify the new permissions. The numeric mode is composed of four digits, each representing a different set of permissions: the first digit is for the special permissions, such as setuid, setgid, and sticky bit; the second digit is for the user permissions; the third digit is for the group permissions; and the fourth digit is for the others permissions. Each digit can range from 0 to 7, where 0 means no permissions, 1 means execute permission, 2 means write permission, 4 means read permission, and the sum of these values means a combination of permissions. For example, 5 means read and execute permissions, and 6 means read and write permissions.

The setuid permission is a special permission that allows an executable to run with the privileges of the owner of the file, instead of the user who launched it. The setuid permission is represented by the value 4 in the first digit of the numeric mode. For example, to enable the setuid permission on an executable file, use the following command:

chmod 4xxx file

where xxx is the combination of the user, group, and others permissions.

In this question, the executable file is /bin/foo, and the desired permissions are:

• setuid permission enabled
• user permissions: read, write, and execute
• group permissions: read and execute
• others permissions: read and execute

Therefore, the numeric mode for these permissions is 4755, where:

• 4 means setuid permission enabled
• 7 means user permissions: read, write, and execute
• 5 means group permissions: read and execute
• 5 means others permissions: read and execute

The correct command to enable the setuid permission on /bin/foo with these permissions is:

chmod 4755 /bin/foo

This command will change the permissions of /bin/foo to -rwsr-xr-x, where the s in the user section indicates the setuid permission.

The other options are not correct because:

• A. chmod 1755 /bin/foo: This command will enable the sticky bit, not the setuid permission, on /bin/foo. The sticky bit is another special permission that prevents users from deleting or renaming files that they do not own in a shared directory. The sticky bit is represented by the value 1 in the first digit of the numeric mode. For example, to enable the sticky bit on a directory, use the following command:

chmod 1xxx directory

where xxx is the combination of the user, group, and others permissions.

• C. chmod u-s /bin/foo: This command will disable the setuid permission, not enable it, on /bin/foo. The u-s option is a symbolic mode that means remove the setuid permission from the user permissions. For example, to disable the setuid permission on an executable file, use the following command:

chmod u-s file

• D. chmod 755+s /bin/foo: This command is not valid because it mixes the numeric and the symbolic modes, which are not compatible. The 755 is a numeric mode that means user permissions: read, write, and execute; group permissions: read and execute; others permissions: read and execute. The +s is a symbolic mode that means add the setuid and setgid permissions to the user and group permissions, respectively. The chmod command does not accept both numeric and symbolic modes at the same time, and it will fail with an error message saying:

chmod: invalid mode: ‘755+s’ Try ‘chmod --help’ for more information.

References:

• SetUID, SetGID, and Sticky Bits in Linux File Permissions - GeeksforGeeks
• How to use special permissions: the setuid, setgid and sticky bits - Linux Tutorials - Learn Linux Configuration
• chmod(1): change file mode bits - Linux man page