Dependencies

Dependencies in Linux refer to software packages, libraries, or files that other programs require to function properly. Understanding dependency management is crucial for system administration, software installation, and troubleshooting package conflicts.

Key Concepts

Package Dependencies: Software requirements needed for installation
Library Dependencies: Shared libraries (.so files) programs need
Dependency Resolution: Automatic handling of requirements
Circular Dependencies: When packages depend on each other
Broken Dependencies: Missing or incompatible requirements

Package Manager Commands

APT (Debian/Ubuntu)

apt install package-name apt-cache depends package-name apt-cache rdepends package-name

YUM/DNF (Red Hat/Fedora)

yum install package-name yum deplist package-name dnf repoquery --requires package-name

Common Dependency Commands

APT System

apt-cache depends - Show package dependencies apt-cache rdepends - Show reverse dependencies apt --fix-broken install - Fix broken dependencies apt autoremove - Remove unused dependencies

YUM/DNF System

yum deplist - List package dependencies yum history - View installation history dnf repoquery --whatrequires - Find what needs package

Practical Examples

Example 1: Check Package Dependencies

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apt-cache depends firefox
firefox
  Depends: libc6
  Depends: libgtk-3-0
  Depends: libx11-6

Shows what firefox needs to run

Example 2: Find What Depends on Package

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apt-cache rdepends libssl1.1
libssl1.1
Reverse Depends:
  openssh-server
  apache2
  mysql-server

Shows packages that need libssl1.1

Example 3: Fix Broken Dependencies

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sudo apt --fix-broken install

Attempts to resolve dependency conflicts

Example 4: Check Library Dependencies

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ldd /usr/bin/ls
linux-vdso.so.1 => (0x00007fff8d1fe000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6

Shows shared libraries a binary needs

Use Cases

Installing software packages safely
Troubleshooting application startup issues
Planning system upgrades
Creating custom software distributions
Resolving package conflicts
System cleanup and optimization

ldd - Show shared library dependencies dpkg -l - List installed packages (Debian) rpm -qa - List installed packages (Red Hat) ldconfig - Configure library cache pkg-config - Retrieve compilation flags

Library Dependency Tools

objdump -p binary - Show binary dependencies readelf -d binary - Display dynamic section nm -D library.so - List dynamic symbols

Tips & Troubleshooting

Common Issues

Missing libraries: Use ldd to identify, install dev packages
Version conflicts: Check with apt list --installed
Broken packages: Run apt --fix-broken install
Circular deps: May need manual intervention

Best Practices

Always check dependencies before major upgrades
Use virtual environments for development
Keep package manager databases updated
Document custom installations
Test dependency changes in staging first

Performance Notes

Too many dependencies slow system startup
Use apt autoremove regularly to clean unused packages
Consider static linking for critical applications
Monitor disk space usage from dependencies

Security Considerations

Keep all dependencies updated for security patches
Audit dependency chains for vulnerabilities
Use official repositories when possible
Verify package signatures before installation