File Info Explained — Metadata, Permissions, and TimestampsFile information — often called “file info” — is the set of data that describes a file beyond its actual contents. Understanding file info is important for managing files securely, troubleshooting problems, organizing large collections of data, and automating workflows. This article explains the most important components of file info: metadata, permissions, and timestamps. It also covers how different operating systems handle these items, common tools to view and edit them, and practical tips for everyday use.
What is File Metadata?
Metadata is data about data. For a file, metadata provides descriptive details that help identify, classify, and manage the file without opening it. File metadata typically includes:
- File name and size
- File type (MIME type or extension)
- Creator/author information (when available)
- Application-specific metadata (for example, EXIF data in images, ID3 tags in audio files, or document properties in office files)
- Checksums and hashes (MD5, SHA-1, SHA-256) used to verify integrity
- Extended attributes and custom key/value pairs supported by some file systems
Why metadata matters:
- Enables search and indexing (e.g., desktop search, media libraries).
- Supports automated processing (scripts that select files by type, date, or tag).
- Stores provenance and copyright/attribution details.
- Can leak sensitive information (e.g., GPS coordinates in photos).
File Permissions: Who Can Do What
File permissions control which users and processes can read, write, or execute a file. Permissions are a core part of operating system security.
Common permission models:
- POSIX (Unix, Linux, macOS): Uses user/group/other and read/write/execute bits. A typical representation is rwxr-xr– (owner has read/write/execute; group has read/execute; others have read).
- ACLs (Access Control Lists): Provide more fine-grained control by listing specific users and groups with explicit permissions.
- Windows NTFS permissions: Use a combination of standard and advanced permissions (Read, Write, Execute, Modify, Full Control) and are managed via Access Control Entries (ACEs) in an ACL.
Key concepts:
- Owner: The user who owns the file and usually has the right to change permissions.
- Group: A set of users that can share permissions.
- Execute bit: For scripts and binaries, determines whether a file can be run. For directories, it controls the ability to traverse/list contents depending on other bits.
- Inheritance: On many systems, directories can pass default permissions to newly created files and subdirectories.
Tools and commands:
- Linux/macOS: ls -l, chmod, chown, getfacl/setfacl
- Windows: icacls, attrib, File Explorer security tab
Security considerations:
- Restrict write permissions to prevent unauthorized modification.
- Avoid setting files or directories to world-writable (777 on Unix) unless necessary and monitored.
- Regularly audit ACLs on sensitive directories.
Timestamps: When Things Happened
Files typically have several timestamps that record lifecycle events. The most common are:
- Creation time (ctime on Windows; on some Unix filesystems, birth time or btime) — when the file was created.
- Modification time (mtime) — when file contents were last modified.
- Access time (atime) — when the file was last read/accessed.
- Status change time (ctime on Unix) — when metadata or ownership/permissions changed (different from creation time on Unix).
How timestamps behave:
- Editing file contents updates mtime.
- Changing permissions or ownership updates ctime (Unix).
- Reading a file can update atime, but many systems mount filesystems with options (noatime, relatime) to avoid frequent atime updates for performance.
- Copying a file may result in different creation times depending on OS and copy method; some tools preserve timestamps (cp -p, rsync -a).
Viewing and modifying timestamps:
- Linux/macOS: stat, ls -l (shows mtime), touch (change mtime/atime)
- Windows: File Explorer details pane, PowerShell Get-Item/Set-ItemProperty, fsutil
Forensic and backup implications:
- Timestamps are valuable in forensics to reconstruct timelines but can be altered intentionally or by file transfers.
- Backup tools use mtime to determine which files changed and need to be copied.
OS Differences and Special Cases
Windows:
- Uses NTFS which supports detailed ACLs and an explicit creation timestamp.
- Metadata support via Alternate Data Streams (ADS) and file properties stored by applications.
macOS:
- HFS+ and APFS both support extended attributes and resource forks. APFS includes strong snapshot and cloning features that affect how timestamps and metadata might be preserved.
Linux:
- Variety of filesystems (ext4, XFS, Btrfs) with differing support for birth time and extended attributes.
- Extended attributes (xattr) and SELinux labels can add more metadata and control.
Mobile platforms:
- iOS and Android store app-level metadata and often strip or manage some metadata (especially location) differently for privacy.
Cloud storage:
- Many cloud services add their own metadata (who uploaded, version history, shared status) which may be separate from local filesystem metadata.
Practical Tools and Examples
Viewing metadata:
- Images: exiftool image.jpg — shows EXIF, IPTC, XMP, and many other tags.
- Audio: eyeD3 or id3v2 for MP3 tags; ffprobe for media container metadata.
- Documents: libreoffice –writer –cat (or file properties in office apps) and exiftool supports many document formats.
- Generic: stat filename, ls -l, getfattr/getfacl on Linux; PowerShell Get-Item and Get-Acl on Windows.
Changing metadata:
- exiftool -AllDates=“2020:01:01 12:00:00” image.jpg
- Set permissions: chmod 644 file.txt; chown user:group file.txt
- Touch timestamp: touch -t 202001011200 file.txt
Automating extraction:
- Use scripts with exiftool, ffprobe, or platform commands to batch-extract metadata into CSV/JSON for indexing or archival.
Privacy and Security: What to Watch For
- Photos often contain GPS coordinates and device identifiers in EXIF; strip them before sharing publicly (exiftool -gps:all= image.jpg).
- Office documents may contain author names, revision histories, and hidden comments—use document sanitization features before distribution.
- Checksums and signatures help verify file integrity and detect tampering. Use SHA-256 or stronger where possible.
- Be cautious when changing timestamps and metadata for evidence or compliance—document the changes and reasons.
Common Tasks & Quick Commands
- Show detailed info (Linux/macOS): stat filename
- Show long listing with permissions: ls -l filename
- Change permissions (Unix): chmod 640 filename
- Change owner (Unix): chown alice:staff filename
- View EXIF (images): exiftool photo.jpg
- Remove GPS from photo: exiftool -gps:all= photo.jpg
- Preserve timestamps during copy (rsync example): rsync -a source/ dest/
Troubleshooting Tips
- If a file appears to have wrong timestamps after copying, try copying with preservation flags (cp -p, rsync -a) or use tools that preserve metadata.
- When a file won’t execute on Unix, check the execute bit (ls -l) and set with chmod +x.
- If permission changes don’t apply as expected, check for ACLs or SELinux/AppArmor policies that may override simple mode bits.
- For inconsistent metadata across platforms, consider export/import using standardized formats (XMP for images/documents, ID3 for audio).
Summary
Understanding file info—metadata, permissions, and timestamps—makes file management more reliable, secure, and efficient. Metadata helps describe and index files; permissions protect them from unauthorized actions; timestamps provide a timeline of activity. Different operating systems and file systems handle these elements differently, so pick the right tools and be mindful of privacy and security when viewing or modifying file info.