What are the main macOS error domains?

macOS layers several error systems. OSStatus is a signed 32-bit code used by Core Foundation, Security (errSec…), and legacy Carbon APIs. Mach kernel calls return kern_return_t values (KERN_…). And the BSD layer uses the same POSIX errno values as other Unix systems. NSError often wraps one of these under a domain string.

Why are some OSStatus codes negative?

OSStatus is a signed integer, and many classic codes are negative — for example -43 (fnfErr, file not found) or paramErr (-50). Security framework codes such as errSecItemNotFound (-25300) are large negative numbers. The sign is part of the value, so search with the minus sign included.

How do I see the error behind a failed call?

In code, check the OSStatus or kern_return_t return value, or read the NSError out-parameter and inspect its domain and code. On the command line, Apple's 'macerror ' utility prints the text for many OSStatus values, and Console.app shows framework errors in the unified log.

Is errno used on macOS too?

Yes. The BSD/POSIX layer under macOS uses standard errno values like ENOENT (2) and EACCES (13), identical in meaning to Linux. System calls set errno the same way, and strerror/perror translate it. Higher-level frameworks usually surface OSStatus or NSError instead.

Is my input sent anywhere?

No. The code table ships with the page and every lookup happens in your browser.

macOS Error Codes — Gera Tools

Email me this result

Get this tool's output sent to your inbox, plus one useful tool a week. No spam, unsubscribe any time.

Decode a macOS error code across all three domains

macOS reports failures through several systems: signed OSStatus codes from Core Foundation, Security, and Carbon; kern_return_t values from the Mach kernel; and plain POSIX errno from the BSD layer. A bare number like -25300 or -43 is meaningless until you know which domain it came from. This tool takes a number or a symbolic name and returns the domain, meaning, and a fix hint.

How it works

The page carries a curated table of common codes, each tagged with its domain (OSStatus, Mach, or POSIX), the symbolic name, its numeric value, the meaning, and a hint. Your input is normalised: a 0x prefix is parsed as hexadecimal, otherwise a signed integer is parsed (so -43 matches fnfErr). Numeric queries match the stored value exactly. Text queries match the symbolic name and the meaning case-insensitively, so keychain or not found group related Security and file errors together.

Tips and notes

OSStatus is signed — include the minus sign when searching classic codes (-50, -43) and Security codes (errSecItemNotFound, -25300). Apple’s macerror command-line tool translates many OSStatus values, and Console.app plus the unified log (log show) surface framework errors with their domain. For Mach codes, mach_error_string gives text at runtime. The BSD layer uses the same errno values as any Unix, so a 2 from a low-level call is ENOENT. This table covers common cases; Apple’s headers (MacErrors.h, SecBase.h, mach/kern_return.h) are authoritative for the full set.