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Hands-on Lab·LPIC-1

SUID, sudo, and who can do what

Objective 110.1 asks you to find files with the SUID bit set and to explain what sudo grants. This guide starts from the puzzle that makes SUID make sense - /etc/shadow is unreadable to ordinary users, yet they can change their own passwords - and works outwards to auditing every such program on the machine and reading the sudo rule that applies to your own account.

102: Security Guide 23 of 33 Intermediate

One Debian-family host. Everything is read-only except the GPG demonstration, which works inside a directory created and removed by the page.
Server NameIP AddressOSRolesCPURAMHDD
LPIC1-A01192.168.0.76Ubuntu 26.04 LTSDebian-family host - dpkg and apt, which objective 102.4 names2 Core4 GB50 GB

This guide includes

Use this for the objective that asks you to find SUID files and explain them. This matters because two facts about passwd cannot both be true without that bit - which is what finally makes it make sense.

Before you start

  1. The puzzle that makes SUID make sense

  2. Auditing every program with that power

  3. What sudo actually grants

  4. Accounts that cannot log in, and who has

Official sources

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