75 of 153 questions · Page 2/3 · Lxp System Management topic · Answers revealed
An administrator wants to start a long-running script in the background so that it continues running even after logging out. Which command should be used?
Correct: nohup allows process to survive logout; & runs in background.
Why this answer
nohup prevents the process from receiving SIGHUP when the terminal closes. & runs it in background.
An administrator wants to change the priority of a running process with PID 1234 to a lower priority (nicer). The current nice value is 0. Which command will set the nice value to 10?
Correct: renice sets the nice value for the process.
Why this answer
The `renice` command is used to alter the scheduling priority of an already running process. By default, a process starts with a nice value of 0. Running `renice 10 -p 1234` sets the nice value to 10, which is a lower priority (more 'nice') because the kernel adds this value to the dynamic priority calculation, giving the process less CPU time.
Exam trap
Cisco often tests the distinction between `renice` (for running processes) and `nice` (for launching a new process with a modified priority), and candidates may confuse `renice` with `nice` or think `kill` can change priority via signal numbers.
How to eliminate wrong answers
Option B is wrong because `nice -n 10 kill 1234` attempts to run the `kill` command with a nice value of 10, but `kill` does not change the priority of an existing process; it sends signals. Option C is wrong because `chrt -p 10 1234` sets the real-time scheduling policy and priority (via the `-p` flag with a priority value), not the nice value; `chrt` manipulates the SCHED_FIFO or SCHED_RR policy, not the conventional nice/renice mechanism. Option D is wrong because `kill -10 1234` sends signal 10 (SIGUSR1 by default on Linux) to the process, which has no effect on its nice value or scheduling priority.
A technician is troubleshooting a service that fails to start. The service file is located in /usr/lib/systemd/system. Which THREE commands can be used to investigate the service's status and logs? (Choose three.)
Shows logs for the service.
Why this answer
systemctl status shows service status; journalctl -u shows logs for the unit; journalctl -f follows new log entries. systemctl start attempts to start but not investigate; systemctl enable enables at boot.
A Linux administrator needs to locate all files in the /var directory that have been modified within the last 30 minutes and are larger than 10MB. Which command accomplishes this task?
Correct: -mmin -30 matches files modified less than 30 minutes ago, and -size +10M matches files larger than 10MB.
Why this answer
The find command with -mmin and -size options can locate files based on modification time and size. -mmin -30 finds files modified less than 30 minutes ago, and -size +10M finds files larger than 10MB.
Which three directories are required by the FHS to be present on a Linux system? (Select THREE.)
Essential user binaries.
Why this answer
/bin, /etc, and /dev are essential FHS directories. /opt is optional, /proc is a virtual filesystem, /mnt is for temporary mounts but not always present.
A Linux administrator needs to locate all files in the /etc directory that have been modified in the last 24 hours and are not owned by root. Which two commands can be combined to achieve this? (Select TWO.)
Correct: finds files modified in last 24 hours not owned by root.
Why this answer
find with -mtime 0 finds files modified in the last 24 hours; -not -user root excludes root-owned files. The -exec option executes ls -l to list details.
Which command displays real-time information about running processes, including CPU and memory usage, and updates the display dynamically?
top provides real-time dynamic process information.
Why this answer
top displays a dynamic real-time view of running processes and system resource usage.
A user wants to create a hard link to a file. Which three conditions must be true for a hard link to be created successfully? (Choose three.)
Correct: hard links cannot cross filesystem boundaries.
Why this answer
Hard links cannot span filesystems, cannot link to directories (except by root with special options), and the target must exist. They share the same inode.
A technician needs to apply an access control list (ACL) to a file to grant read and write permissions to a specific user. Which two commands are used to manage ACLs? (Choose two.)
Sets ACL entries.
Why this answer
setfacl sets ACLs, getfacl retrieves them.
An administrator needs to find all files in /etc that have the SUID bit set. Which find command is correct?
Correct: /4000 matches files with SUID set.
Why this answer
The SUID bit is represented by the permission 4000. -perm /4000 checks if any of the bits in 4000 are set (SUID).
A user reports that a specific process is consuming too much CPU. The administrator needs to change the priority of the process to a lower value (nicer). Which command sequence is appropriate?
Correct: renice +10 increases niceness (lower priority).
Why this answer
renice changes the priority of an already running process by PID.
A Linux administrator needs to view the last 10 lines of a log file named 'syslog'. Which command should be used?
Tail -10 shows the last 10 lines of the file.
Why this answer
The 'tail' command outputs the last lines of a file; by default it shows 10 lines.
A Linux engineer is troubleshooting a boot issue. The system boots to a command-line interface but does not start the graphical interface. Which systemd target should be set as default to boot into a graphical environment?
This target boots into a graphical environment.
Why this answer
graphical.target is the systemd target for a graphical user interface.
A Linux administrator wants to search for all occurrences of the word 'ERROR' in log files under /var/log, ignoring case, and also print the line numbers. Which command should be used?
Correct: -r recursive, -i ignore case, -n line numbers.
Why this answer
grep -rin 'ERROR' /var/log searches recursively, ignores case, and prints line numbers. -i for case-insensitive, -n for line numbers, -r for recursive.
A Linux administrator needs to remove a package installed via RPM and all its configuration files. Which command should the administrator use?
Correct: rpm -e removes the package and its configuration files.
Why this answer
rpm -e --nodeps removes the package but ignores dependencies; rpm -e --allmatches removes all versions; rpm -e package removes the package but leaves config files; rpm -V verifies package. To remove config files, use -e with --nodeps may still leave config. Actually, rpm -e removes the package and config files by default.
But among options, only rpm -e package is the correct removal; the other options are either verification or incorrect. However, the question asks to remove and all config files. rpm -e does that. Option A is rpm -V (verify).
Option B is rpm -e --nodeps (ignores dependencies, still removes config). Option C is rpm -e --allmatches (removes all versions). Option D is rpm -e package (standard removal).
All three removal options remove config? Actually rpm -e removes config files. So the best answer: rpm -e package. But note: --nodeps might be used if dependencies are a problem, but the question doesn't mention dependencies.
So the most straightforward is rpm -e package.
An administrator needs to permanently disable a systemd service from starting at boot. Which two commands can achieve this? (Choose two.)
Removes symlinks to prevent startup at boot.
Why this answer
systemctl disable and systemctl mask both prevent a service from starting at boot, but mask also prevents manual start.
A Linux administrator wants to search for the pattern 'ERROR' in all files under /var/log, ignoring case, and display line numbers. Which THREE options should be used with the grep command? (Select THREE).
Ignores case distinctions.
Why this answer
grep -r for recursive, -i for case-insensitive, -n for line numbers.
A process is running with a nice value of 5. The system administrator wants to increase its priority (lower the nice value) to -5 but is not the owner of the process. What must the administrator do first to achieve this?
Correct: renice requires root to change priority of another user's process.
Why this answer
Only root can increase priority (lower nice value) of another user's process. The administrator must use sudo or become root to run renice. Option A is incorrect because nice command starts a new process.
Option C is correct: run renice with sudo. Option D is incorrect because renice -n +10 would lower priority (increase nice).
A technician needs to replace the string 'oldhost' with 'newhost' in the file /etc/hostname. Which sed command will perform this change in-place?
Correct: -i for in-place, s/oldhost/newhost/g for substitution.
Why this answer
sed -i with s/pattern/replacement/ does an in-place substitution.
An administrator suspects that a malicious process is running and wants to list all processes, including those without a controlling terminal, and see their full command line. Which two commands can provide this information? (Select TWO.)
Shows all processes with full command line.
Why this answer
ps aux shows all users, all processes, including those without tty, and includes the full command line. ps -ef also shows full listing with command line.
A user reports that a script in /home/user/script.sh fails to execute. The output of 'ls -l script.sh' is '-rw-r--r-- 1 user user 1024 Apr 1 10:00 script.sh'. Which command should be used to make the script executable for all users?
Correct: a+x adds execute permission for all users (owner, group, others).
Why this answer
The file is currently not executable (rw-r--r--). To add execute permission for all users, use chmod a+x or chmod +x.
An administrator runs the command `ls -l file.txt` and sees the permissions `-rwsr-xr-x`. What special permission is set on this file?
The 's' in owner execute indicates SUID.
Why this answer
The 's' in the owner execute position indicates the SUID (Set User ID) permission is set.
An administrator wants to view the contents of a compressed log file /var/log/syslog.2.gz without decompressing it to disk. Which two commands can be used to display the file contents? (Select TWO).
Correct: zcat decompresses and outputs to stdout.
Why this answer
zcat and gzcat (if available) decompress to stdout; some systems use zcat or gzip -dc.
Which command creates a symbolic link named 'link.txt' that points to 'original.txt'?
Correct syntax for symbolic link.
Why this answer
ln -s target link_name creates a symbolic link.
A user needs to view the first 15 lines of a large log file. Which command is most appropriate?
Correct: head -n 15 shows the first 15 lines.
Why this answer
head -n 15 filename displays the first 15 lines of a file.
An administrator wants to gather information about disk usage for a specific directory and its subdirectories. Which TWO commands can be used for this purpose? (Choose two.)
Summarizes total disk usage of the directory.
Why this answer
du -sh /path gives a summary of total disk usage. du -h /path shows disk usage for each subdirectory in human-readable format. df shows filesystem-level usage, not directory-level.
A file has permissions rwxr-x--- and is owned by user alice and group devs. Which command would add the SUID bit while preserving existing permissions?
Adds SUID bit without altering other permissions.
Why this answer
chmod u+s adds the SUID bit. The symbolic mode 'u+s' sets the SUID without changing the existing permission bits.
An administrator needs to update the package cache and upgrade all installed packages on a Debian-based system. Which TWO commands are appropriate for this task? (Select TWO.)
Updates the package index.
Why this answer
apt update refreshes the package cache; apt upgrade upgrades all packages. apt-get update and apt-get upgrade are also valid. The question asks for two commands; typically the sequence is update then upgrade. Both apt and apt-get are acceptable.
A technician is troubleshooting a service that fails to start at boot. Which systemctl command should be used to ensure the service starts automatically on subsequent boots?
Enables the service to start at boot.
Why this answer
systemctl enable creates symlinks so the service starts at boot. The status shown by is-enabled confirms if it is enabled.
A system administrator needs to set the umask so that newly created files have permissions of 644 and directories have permissions of 755. Which umask value should be set?
Correct: umask 022 subtracts group and others write permission, resulting in 644 for files and 755 for directories.
Why this answer
Default base permissions are 666 for files and 777 for directories. To get 644 (rw-r--r--) for files: 666 - 644 = 022. To get 755 (rwxr-xr-x) for directories: 777 - 755 = 022.
So umask 022 works for both.
A system administrator is investigating a performance issue. Which THREE commands can be used to monitor running processes in real-time? (Select THREE).
zgrep searches within compressed files.
Why this answer
The commands zcat, zless, and zgrep are specifically designed to display the contents of compressed files without decompressing them. zcat outputs the decompressed file to stdout, zless allows interactive viewing, and zgrep searches within compressed files. In contrast, cat and less cannot directly handle compressed files and would output binary garbage or fail.
Given an ACL entry 'u:john:rwx' on a file, which command would remove only the ACL entry for user john without affecting other ACL entries?
-x removes the specified entry.
Why this answer
setfacl -x removes a specific ACL entry. The syntax 'u:john' removes the ACL for user john.
A Linux administrator needs to change the permissions of a file to be readable and writable by the owner, readable by the group, and no access for others. Which command accomplishes this?
Correct: 640 gives owner rw, group r, others none.
Why this answer
The octal representation 640 sets owner read/write (6), group read (4), and others none (0).
A system running systemd is failing to boot properly. The administrator wants to boot into an environment with only the essential services for troubleshooting. Which systemd target should be selected at boot?
Correct: rescue.target provides a single-user shell with basic services.
Why this answer
rescue.target starts a minimal system with root filesystem mounted read-only and basic services.
Which of the following commands can be used to display the contents of a file one page at a time? (Choose two.)
Correct: less is a pager.
Why this answer
The `less` command is a pager that displays file contents one screen at a time, allowing both forward and backward navigation. It is designed for viewing large files interactively, loading only the visible portion into memory for efficiency.
Exam trap
The trap here is that candidates may confuse `cat` as a pagination tool because it displays file contents, but it lacks any paging or interactive control, while `head` and `tail` are often mistakenly thought to paginate because they show a subset of lines.
A system administrator wants to ensure that a service starts automatically at boot time using systemd. Which command should be used?
Correct: enable sets the service to start at boot.
Why this answer
systemctl enable creates symlinks to make the service start at boot.
A user wants to run a command that will continue running even after the user logs out. Which command should be used?
Correct: nohup prevents the command from being terminated on logout, & backgrounds it.
Why this answer
nohup makes the command immune to hangups and runs in the background.
A system administrator wants to display a list of all currently running processes, including those of other users, with full command lines. Which TWO commands can achieve this? (Select TWO.)
Correct: shows all processes with user info and full command line.
Why this answer
ps aux and ps -ef both show all processes with full command lines. top and htop show dynamic views but not in a static list format. pstree shows process tree.
An administrator needs to view the last 20 lines of the systemd journal for the 'sshd' service. Which command should be used?
Correct: -u specifies unit, -n limits lines to 20.
Why this answer
journalctl -u sshd -n 20 shows the last 20 lines of the journal for the sshd unit.
A system administrator runs the command 'chmod 4755 /usr/local/bin/backup'. What effect does this have on the file?
SUID bit is set with 4xxx, permissions are 755.
Why this answer
The 4 in the first digit sets the SUID bit, so the file runs with the owner's permissions. 755 sets rwxr-xr-x.
An administrator wants to display the last 20 lines of a log file and also write those lines to a file called recent.log. Which command should be used?
Correct: tail outputs last 20 lines, tee sends to both stdout and recent.log.
Why this answer
tail -n 20 file | tee recent.log displays the last 20 lines and writes them to recent.log. tee is used to split output to file and stdout.
A technician needs to find all files in /home that have the SUID or SGID permission set. Which THREE commands can accomplish this? (Choose three.)
Combines -perm -4000 and -perm -2000 with OR.
Why this answer
find /home -perm /6000 matches files with either SUID (4000) or SGID (2000). -perm -4000 matches SUID only, -perm -2000 matches SGID only. The / notation matches any of the bits.
A developer wants to change all occurrences of 'foo' to 'bar' in a configuration file and save the changes in-place. Which sed command should be used?
Correct: -i enables in-place editing.
Why this answer
sed -i 's/foo/bar/g' file performs an in-place global substitution. The -i flag edits the file directly.
An administrator needs to find the line number of the first occurrence of the string 'ERROR' in a log file, ignoring case. Which command is most appropriate?
-i for case insensitive, -n for line numbers.
Why this answer
grep -in 'error' logfile will output the line numbers with matches, ignoring case. The first line will be shown first if no other sorting is applied.
A Linux administrator needs to add an ACL entry to grant read permission to a user named 'jdoe' on a file. Which TWO commands can be used to achieve this? (Select TWO).
This adds an ACL entry for user jdoe with read permission.
Why this answer
Both setfacl -m and setfacl --modify can be used to modify ACLs. The -m option is the short form, and --modify is the long form.
Which directory in the Linux filesystem contains essential user command binaries that are needed for booting and repairing the system?
Correct: /bin contains essential binaries like ls, cp, etc., needed during boot.
Why this answer
/bin contains essential command binaries required for booting and recovery.
An administrator notices that a service named 'httpd' is not running. They want to check its current status and, if inactive, start it. Which set of systemctl commands should be used?
Correct sequence.
Why this answer
systemctl status httpd shows the status; if inactive, systemctl start httpd starts it. The other options have incorrect commands or syntax.
An administrator wants to find all files in the current directory tree that are larger than 100 MB and have the .log extension. Which find command will accomplish this?
Correct: finds .log files larger than 100 MB.
Why this answer
-size +100M finds files larger than 100 MB; -name '*.log' matches .log extension. Option A uses -type f but missing -name. Option B has -size +100MB (should be M).
Option D uses -size -100M (smaller).
Which command is used to display the contents of a compressed log file without decompressing it?
zcat reads compressed files and outputs to stdout.
Why this answer
zcat is used to view compressed files; it is equivalent to gunzip -c.
A user wants to view the contents of a text file one page at a time. Which two commands can be used? (Choose two.)
less is a pager with backward and forward navigation.
Why this answer
less and more are pagers that display content one screen at a time.
A Linux administrator needs to find all files in /var/log that have been modified within the last 7 days and are larger than 10 MB. Which find command accomplishes this?
Correct: -mtime -7 for last 7 days, -size +10M for larger than 10 MB.
Why this answer
The -mtime -7 option matches files modified less than 7 days ago, and -size +10M matches files larger than 10 MB.
A technician needs to replace all occurrences of '192.168.1.' with '10.0.0.' in the file /etc/network/interfaces and save the changes. Which command accomplishes this?
Correct use of -i for in-place substitution.
Why this answer
sed -i 's/192\.168\.1\./10.0.0./g' /etc/network/interfaces uses in-place editing with the substitute command globally.
Which directory in the Filesystem Hierarchy Standard (FHS) contains essential user commands available to all users, such as 'ls' and 'cp'?
Correct: /bin holds essential user commands.
Why this answer
/bin contains essential user binaries. /sbin is for system binaries (usually root). /usr/bin contains non-essential user binaries. /opt is for optional software.
A technician needs to replace the string 'old_config' with 'new_config' in the file /etc/app.conf and save the changes in place. Which sed command accomplishes this?
Correct usage of in-place substitution globally.
Why this answer
The -i flag edits the file in place, and the s///g substitution replaces all occurrences.
An administrator wants to change the default systemd target to multi-user.target so the system boots to a text console. Which command should be used?
Correct command to set default target.
Why this answer
systemctl set-default multi-user.target sets the default target. systemctl isolate changes the current target but not the default. enable and mask are for services, not targets.
An administrator is troubleshooting a boot issue. The system boots to a console with limited functionality. Which systemd target should be used to bring up the system with network and multi-user support?
Correct: multi-user.target boots to a text console with network.
Why this answer
multi-user.target provides a non-graphical multi-user system with network.
An administrator needs to grant read and write access to the 'developers' group on a directory while preserving existing permissions for the owner and others. Which TWO commands can be used to modify ACLs? (Choose two.)
Correct: modifies ACL to grant rw to group.
Why this answer
setfacl -m g:developers:rw sets ACL entry. getfacl displays ACLs but does not modify. chmod changes standard permissions, not ACLs. setfacl -x removes ACLs. setfacl -b removes all ACLs.
A technician needs to create a new ext4 filesystem on /dev/sdb1 and mount it persistently at /mnt/data. Which set of commands accomplishes this?
Correct sequence.
Why this answer
mkfs.ext4 /dev/sdb1 creates the filesystem. Adding an entry to /etc/fstab ensures persistent mount. mount -a mounts all filesystems in fstab.
An administrator needs to create a hard link to an existing file. Which two statements are true about hard links? (Choose two.)
They are additional directory entries pointing to the same data.
Why this answer
Hard links share the same inode and cannot span filesystems. They cannot link to directories.
An administrator wants to find all files larger than 100MB in the /var directory. Which command should be used?
This command finds files larger than 100MB.
Why this answer
The find command with -size +100M correctly locates files larger than 100MB.
A system administrator is troubleshooting a service that fails to start at boot. The system uses systemd. Which of the following commands would the administrator use to check the service's status and view its recent log entries?
Correct: status shows service state and recent logs; journalctl -n 50 shows last 50 lines.
Why this answer
The correct answer is B. 'systemctl status service' displays detailed status of the service, including recent logs. 'journalctl -n 50' shows the last 50 journal entries. Together, they provide both status and recent logs. Option A uses 'systemctl is-active', which only returns active/inactive, not detailed status.
Option C lists failed units and error-level logs, not specific to the service. Option D also uses 'systemctl is-active' (boolean) and 'journalctl -n 50' without focusing on the service. Therefore, B is the best choice.
A process is consuming excessive CPU and needs to be terminated immediately. The PID is 1234. Which command will terminate the process with the most forceful signal?
Correct: SIGKILL immediately terminates.
Why this answer
kill -9 (SIGKILL) forcibly terminates the process. SIGTERM (15) is graceful; SIGHUP (1) reloads config; SIGSTOP (19) suspends.
A system administrator needs to monitor real-time process information and system resource usage. Which two commands can be used for this purpose? (Choose two.)
top shows real-time process list and resource usage.
Why this answer
top and htop are interactive process viewers that show real-time updates.
Which command is used to display the current process hierarchy in a tree format?
pstree displays processes in a tree hierarchy.
Why this answer
ps aux shows all processes with details, but pstree shows them in a tree format, which is useful for visualizing parent-child relationships.
Which command will display the disk usage of each directory in the current directory, in human-readable format?
Correct: du -h displays disk usage for directories in human-readable format.
Why this answer
The `du -h` command displays disk usage for each directory in the current directory, with the `-h` flag converting sizes into human-readable formats (e.g., K, M, G). This is the correct tool for per-directory disk usage reporting.
Exam trap
The trap here is that candidates confuse `df -h` (filesystem-level usage) with `du -h` (directory-level usage), often picking `df -h` because it also shows human-readable output.
How to eliminate wrong answers
Option B is wrong because `fdisk -l` lists partition tables on block devices, not directory-level disk usage. Option C is wrong because `ls -lh` lists file and directory names with sizes, but it does not compute recursive disk usage for directories. Option D is wrong because `df -h` shows filesystem-level free and used space, not per-directory usage.
Which command displays the disk usage of files and directories in a human-readable format (e.g., KB, MB)?
du -h shows disk usage of files/directories with human-readable sizes.
Why this answer
The `du -h` command (disk usage with human-readable flag) recursively summarizes disk usage for files and directories, appending size suffixes like K, M, G for kilobytes, megabytes, and gigabytes. This directly matches the question's requirement to display disk usage in a human-readable format.
Exam trap
The trap here is that candidates confuse `df -h` (filesystem-level free space) with `du -h` (per-file/directory disk usage), or assume `ls -lh` shows disk usage when it actually shows logical file size, not the blocks consumed on disk.
How to eliminate wrong answers
Option A is wrong because `df -h` reports filesystem-level disk space usage (free/used blocks on mounted partitions), not the disk usage of individual files and directories. Option B is wrong because `ls -lh` lists file sizes in human-readable format but does not compute or display disk usage (the actual blocks consumed on disk), which can differ from file size due to sparse files or block allocation. Option C is wrong because `stat -h` is not a valid Linux command; `stat` uses `-c` or `--format` for custom output and does not have a `-h` flag for human-readable sizes.
An administrator needs to apply a set of permissions to an existing directory and all its contents, setting the owner to 'rwx', group to 'rx', and others to '---'. Additionally, newly created files within the directory should inherit the group. Which commands should the administrator run? (Assume the directory is /data, and the group is 'staff'.)
Correct: 750 grants rwxr-x---; chmod g+s sets SGID on directory.
Why this answer
chmod -R 750 /data sets permissions recursively. chmod g+s /data sets the SGID bit so new files inherit the group. The other options are missing SGID or have wrong permissions.
A user wants to create a symbolic link to a file named 'original' in their home directory. Which command creates a symbolic link named 'link'?
Correct: -s for symbolic, original is target, link is name.
Why this answer
ln -s creates a symbolic link; order is target (existing file) then link name.
An administrator wants to display only the second field from a colon-delimited file named 'passwd' using a text processing tool. Which command will achieve this?
Correct: awk sets delimiter and prints field 2.
Why this answer
awk -F: '{print $2}' passwd sets field separator to : and prints second field. cut -d: -f2 also works, but the options include awk. sed is for editing, not field extraction; grep is for pattern matching.
A system administrator needs to remove all files in /tmp that have not been accessed in the last 30 days and are not owned by root. Which two commands, combined, could be used to accomplish this? (Select TWO).
Correct: uses -delete instead of -exec rm, also works.
Why this answer
find with -atime and -not -user root locates files; then use -exec rm or -delete to remove.
An administrator needs to give a user read and write access to a file without changing the file's group or adding the user to any group. Which method should be used?
ACL allows specific user permissions without changing group.
Why this answer
Access Control Lists (ACLs) allow setting permissions for specific users beyond the traditional owner/group/others model, without changing group membership.
A user has a file with permissions set to 644. Which of the following commands will add the setuid permission to the file? (Choose two.)
Correct: symbolic mode for setuid.
Why this answer
chmod u+s file adds setuid via symbolic. chmod 4644 file sets permissions to rwsr--r-- (setuid). The other options: chmod 2644 sets SGID; chmod 1644 sets sticky bit; chmod g+s sets SGID.
Which command displays the current umask value in symbolic mode?
Correct. umask -S shows symbolic mode.
Why this answer
umask -S displays the umask in symbolic (rwx) format. The plain umask shows octal.
An administrator needs to replace all occurrences of 'oldhost' with 'newhost' in the configuration file /etc/hosts. Which command will perform the replacement and save the changes directly to the file?
Correct: -i edits file in-place, s/oldhost/newhost/g replaces all occurrences.
Why this answer
Option D is correct because the `-i` flag (in-place editing) tells `sed` to write the changes directly back to the file specified. Without `-i`, `sed` only prints the modified output to stdout and does not alter the original file. The substitution command `s/oldhost/newhost/g` performs a global replacement of all occurrences of 'oldhost' with 'newhost' on each line.
Exam trap
The trap here is that candidates often forget the `-i` flag for in-place editing, assuming `sed` modifies the file by default, or they confuse `sed`'s stream behavior with editors like `vim` that directly change the file.
How to eliminate wrong answers
Option A is wrong because it omits the `-i` flag, so the replacement is performed on the stream and printed to stdout, but the original /etc/hosts file remains unchanged. Option B is wrong because `awk` by default writes to stdout only; it does not have an in-place editing flag, so the file is not saved. Option C is wrong because `grep -r` recursively searches for 'oldhost' in /etc/hosts (which is a single file, not a directory) and pipes matching lines to `sed`, but `sed` again lacks `-i` and the pipeline only processes matched lines, not the entire file, so the original file is not modified.
A file has permissions set to 2755. Which special permission is enabled, and what does it do?
Correct: SGID on directories.
Why this answer
The permission 2755 includes the SGID (Set Group ID) special permission, indicated by the leading digit '2'. When SGID is set on a directory, new files and subdirectories created within it inherit the group ownership of the directory, rather than the primary group of the user who creates them. This is critical for collaborative environments where multiple users need shared group access.
Exam trap
Cisco often tests the distinction between the numeric representations of special permissions (1=sticky, 2=SGID, 4=SUID) and their specific effects on directories versus files, leading candidates to confuse SGID with SUID or the sticky bit.
How to eliminate wrong answers
Option B is wrong because the leading '2' in 2755 explicitly indicates a special permission (SGID) is set, not just octal 755. Option C is wrong because the sticky bit is represented by a leading '1' (e.g., 1755), not '2', and it restricts file deletion to owners, not group inheritance. Option D is wrong because SUID is represented by a leading '4' (e.g., 4755), and it applies to executable files to run with the owner's privileges, not to directories for group inheritance.
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