Linux Foundation / CNCF LFCS: Linux Foundation Certified System Administrator

Last checked October 22, 2026 against the official Linux Foundation / CNCF exam page.

1. Question 1Essential Commands

   An administrator needs the disk space used by each directory under /srv, shown in human-readable sizes and summarized per directory. Which command should be used?

   1. Alsblk /srv
   2. Bdf -h /srv
   3. Cls -lh /srv
   4. Ddu -sh /srv/*
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   Correct answer: D

   du -sh with a glob reports the total size of each item in human-readable form. df reports filesystem free space rather than per-directory usage, ls -lh shows file sizes without totals, and lsblk lists block devices.

2. Question 2Operation of Running Systems

   An administrator needs to check whether the nginx service starts automatically at boot. Which command answers this?

   1. Asystemctl boot-status nginx
   2. Bsystemctl is-enabled nginx
   3. Csystemd-analyze check nginx
   4. Dsystemctl list-boot nginx
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   Correct answer: B

   systemctl is-enabled reports whether a unit is enabled to start at boot. The other options are not systemctl subcommands for this purpose, and systemd-analyze check validates unit file syntax.

3. Question 3Networking

   Which command lists the TCP sockets that are listening, with the numeric ports and the owning process?

   1. Aping -l
   2. Bss -tlnp
   3. Cifconfig -t
   4. Droute -t
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   Correct answer: B

   ss -tlnp shows listening TCP sockets with numeric addresses and process information when run with sufficient privilege. ifconfig and route do not show listening sockets, and ping -l sets a preload count rather than listing sockets.

4. Question 4User and Group Management

   The user dev must join the docker group while keeping the existing supplementary groups. Which command does this?

   1. Auseradd -g docker dev
   2. Busermod -G docker dev
   3. Cusermod -aG docker dev
   4. Dgroupadd dev docker
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   Correct answer: C

   usermod -aG appends the group to the supplementary list, which keeps the existing memberships. Omitting -a replaces the whole list, groupadd creates a group rather than adding a user, and useradd -g changes the primary group when the account is created.

5. Question 5Storage Management

   An administrator needs a tree view of disks, partitions and their mount points. Which command provides it?

   1. Alsblk
   2. Bfdisk -l /dev/sda
   3. Cdu -h /
   4. Dblkid -t
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   Correct answer: A

   lsblk prints block devices as a tree with sizes and mount points. blkid shows filesystem identifiers, fdisk -l lists partition tables without the mount tree, and du reports directory sizes.