Linux System Management 2

Shadow file - user states - password locks - ulimit - file

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Objectives

• Understand Linux user authentication and shadow file structure
• Analyze locked, disabled, and unset passwords in /etc/shadow
• Practice safe file operations using mv -u and mkdir -p
• Configure and verify user limits with ulimit

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Tree

linux-system-management-2/
├── README.md
├── outputs/
│   ├── 01a-shadow-passwd-d.txt
│   ├── 01b-shadow-passwd-l.txt
│   ├── 02-ulimit-output.txt
│   ├── 02b-ulimit-focused.txt
│   ├── 02c-ulimit-test-dd.txt
│   ├── 03-mv-test-output.txt
│   └── 04-mkdir-test-output.txt
└── screenshots/
    ├── 01a-passwd-d-shadow.png
    ├── 01b-passwd-l-shadow.png
    ├── 02-ulimit-output.png
    ├── 02b-ulimit-focused.png
    ├── 02c-ulimit-test-dd.png
    ├── 03-mv-test-output.png
    └── 04-mkdir-test-output.png

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Execution

Examine /etc/shadow

# Create user and remove password
sudo useradd testuser1
sudo passwd -d testuser1
sudo grep testuser1 /etc/shadow

# Lock the user account
sudo passwd -l testuser1
sudo grep testuser1 /etc/shadow

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Resource Limits

ulimit -a
ulimit -u
ulimit -n

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Enforcing File Size

ulimit -f 100
dd if=/dev/zero of=testfile bs=1M count=2

Failure:
File size limit exceeded (core dumped)

Restored default limit afterward:

ulimit -f unlimited
rm -f testfile

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Test

echo "I am older" > oldfile.txt
sleep 2
echo "I am newer" > newfile.txt
mv -u newfile.txt oldfile.txt
cat oldfile.txt

Content of oldfile.txt replaced only because newfile.txt was newer.

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Recursive Directory Creation

mkdir -p /tmp/testdir1/testdir2/testdir3
ls -R /tmp/testdir1

Nested directory trees

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Summary

Linux+ around user account management, shadow file analysis and essential file operations.

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Next Project

→ linux-system-management-3
Focus: SSH, PXE, DNS, name resolution, and network boot behavior