access / faccessat - glibc

Split from the chapter glibc: stdio and Formatted I/O into the per-function layout; see the method page and the glibc ledger for coverage status.

Signature – int access(const char *path, int mode); int faccessat(int dirfd, const char *path, int mode, int flags); – unistd.h; mode is F_OK/R_OK/W_OK/X_OK.

Libc side – checks real UID/GID (unlike actual opens, which use effective IDs); faccessat adds the dirfd model plus AT_EACCESS (effective IDs) and AT_SYMLINK_NOFOLLOW. GNU extras euidaccess and eaccess check effective IDs by path. Return 0 or -1+errno (EACCES, ENOENT, EROFS, … – full list in the syscall chapter access entry, which also tells the faccessat2 story: the raw faccessat syscall has no flags argument, so pre-2.33 glibc emulated AT_* via fstatat; the installed glibc still exports only faccessat, no faccessat2 symbol). TOCTOU-prone by design.