passwdbyuid

passwdbyuid is a function or utility used in Unix-like systems to retrieve a user account entry from the system's password database by user ID (UID). It typically returns a structured record containing fields such as the login name, password placeholder, UID, GID, user information (GEcos), home directory, and login shell. In POSIX systems the standard API that serves a similar purpose is getpwuid, with a reentrant variant getpwuid_r; passwdbyuid may be a wrapper or a library-specific alias implementing similar semantics.

Usage and behavior: A caller supplies a UID to passwdbyuid. On success, the function returns a pointer to a password-like structure (or fills an output parameter) from which fields such as pw_name, pw_uid, pw_gid, pw_gecos, pw_dir, and pw_shell can be read. On failure, it returns null or signals an error, and errno may indicate the cause (for example, no such user). Some implementations may return a copy of the structure that must be freed by the caller, while others may reuse internal storage, which affects thread safety.

Security considerations: In modern systems the actual password hash is not stored in the public password database but in a shadow file (such as /etc/shadow) accessible only to privileged processes. Accessing user account information via passwdbyuid should be done with appropriate privileges and in accordance with system security policies to avoid exposing sensitive account data.

Availability and compatibility: passwdbyuid is not a standard POSIX function. In environments where it is not provided, getpwuid and getpwuid_r serve equivalent purposes. Always consult the specific library or platform documentation for exact semantics, memory management, and error reporting.

See also: getpwuid, getpwuid_r, /etc/passwd, /etc/shadow, UID, GID.