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truncate Command Cheat Sheet

truncate shrinks or extends the size of each FILE to the specified size.

Synopsis

truncate OPTION... FILE...

Basic Usage

Set Exact Size (-s)

Set file size to exactly 10 bytes.

truncate -s 10 file.txt
- If the file was larger, data is lost. - If smaller, it is extended with null bytes (sparse).

Clear a File (0 bytes)

truncate -s 0 logfile.log
Alternative: > logfile.log

Relative Resizing

Grow by Size (+SIZE)

Increase file size by 1MB.

truncate -s +1M storage.img

Shrink by Size (-SIZE)

Decrease file size by 1KB.

truncate -s -1K storage.img

Sparse Files

truncate does not actually write zero bytes to disk when extending; it creates a "hole".

truncate -s 10G hugefile.img
du -h hugefile.img  # Shows 0 or 4K (actual disk usage)
ls -lh hugefile.img # Shows 10G (apparent size)

Notes

  • Permission: Requires write permission on the file.
  • Reference: Use -r to reference another file's size. 
    truncate -r ref_file.txt target.txt