How to Use the Command 'nix-collect-garbage' (With Examples)

How to Use the Command 'nix-collect-garbage' (With Examples)

The nix-collect-garbage command is a maintenance utility in the Nix package manager. It is used to clean up unnecessary and unused files from the Nix store, which can otherwise accumulate and consume a significant amount of disk space over time. This utility helps in managing storage more efficiently and ensures that only relevant and current store paths are retained on the system. By applying different options with the command, users can tailor garbage collection to meet specific needs, such as deleting only unused paths, simulating deletions to prevent errors, or targeting files older than a certain age.

Use Case 1: Delete All Store Paths Unused by Current Generations of Each Profile

Code:

sudo nix-collect-garbage --delete-old

Motivation:

In the context of the Nix package manager, a “generation” is akin to a snapshot of the Nix environment at a given time. Over time, as software is updated or removed, these generations can become outdated. Store paths that are not associated with any current generation can occupy unnecessary disk space. By deleting store paths unused by current generations, users ensure their system is streamlined and optimized, retaining only essential components. This is particularly beneficial for systems that frequently undergo software changes, helping to maintain a clean and efficient environment.

Explanation:

  • sudo: This command often requires elevated privileges to execute because it deals with system-level data.
  • nix-collect-garbage: Initiates the garbage collection process.
  • --delete-old: This option specifies the deletion of old store paths that are no longer used by any current generation. It targets and removes clutter resulting from software updates and deletions.

Example Output:

Upon execution, the terminal may display:

deleting unused store paths...
these paths will be deleted (0.01 MiB): /nix/store/abcdef123456-sample-package

This output indicates the specific paths slated for deletion and the total amount of disk space to be recovered.

Use Case 2: Simulate the Deletion of Old Store Paths

Code:

sudo nix-collect-garbage --delete-old --dry-run

Motivation:

Before making permanent changes to the system, it’s prudent to understand the extent of those changes. Simulating deletions allows users to preview what would happen if the garbage collection were actually executed. This step is vital for risk-averse users concerned about potential data loss or unexpected removals. By using this command option, users can ensure that critical files are not unintentionally deleted, leading to a safer storage management approach.

Explanation:

  • --delete-old: As previously explained, this option targets store paths unused by any current generations.
  • --dry-run: This powerful option transforms the command into a simulation, showing what the command would delete without actually performing the deletions. It provides a preview to ensure that only the intended paths will be removed.

Example Output:

Upon running this dry-run simulation, the terminal might display:

would delete unused store paths:
these paths would be deleted (0.01 MiB): /nix/store/abcdef123456-sample-package

This output informs the user of which paths would be deleted if the command was run without the --dry-run modifier.

Use Case 3: Delete All Store Paths Older Than 30 Days

Code:

sudo nix-collect-garbage --delete-older-than 30d

Motivation:

Files and data older than a certain threshold, in this case, 30 days, are often deemed obsolete, especially if they have not been interacted with recently. By wiping out older files, users can make substantial savings on disk space and keep the file system uncluttered with outdated data. This use case is particularly beneficial for systems with long retention periods or those undergoing frequent updates and changes.

Explanation:

  • --delete-older-than: This option specifies a time-based criterion for deletions, targeting paths older than a specified age.
  • 30d: This parameter indicates the age of the files to be purged, in this instance, files older than 30 days.

Example Output:

Upon execution, the terminal might show:

deleting store paths older than 30d...
these paths will be deleted (0.05 MiB): /nix/store/ghijkl7891011-other-package

This output indicates the specific paths and the total space to be reclaimed from removing data older than 30 days.

Conclusion:

The nix-collect-garbage command is a powerful tool within the Nix package management ecosystem, providing users a structured way to maintain disk space by removing unnecessary and outdated store paths. Each example outlined above caters to different scenarios and needs—be it regular cleanup, risk-free testing, or age-targeted deletion. Through smart use of these functionalities, system administrators and developers can ensure their environments remain efficient, clean, and devoid of clutter.

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