Stat (system call)

is a Unix system call that queries the file system for metadata about a file. The metadata contains many fields including file type|type], size, ownership, permissions and timestamps.
For example, the [ls|] command uses this system call to retrieve timestamps:

mtime: when last modified
atime: when last accessed
ctime: when last status changed

appeared in Version 1 Unix. It is among the few original Unix system calls to change, with Version 4's addition of group permissions and larger file size.
Since at least 2004, the same-named shell command stat has been available for Linux to expose features of the system call via a command-line interface.

Functions

The C [POSIX library] header, found on POSIX and other Unix-like operating systems, declares stat and related functions.

int stat;
int lstat;
int fstat;

Each function accepts a pointer to a struct stat buffer which the function loads with information about the specified file. As typical for system calls, each function returns 0 on success, or on failure, sets errno to indicate the failure condition and returns −1.
The stat and lstat functions accept a path argument that specifies a file. If the path identifies a symbolic link, stat returns attributes of the link target, whereas lstat returns attributes of the link itself. The fstat function accepts a file descriptor argument instead of a path, and returns attributes of the file that it identifies.
The library has been extended to support large files. Functions stat64, lstat64 and fstat64 load information into a struct stat64 buffer, which supports 64-bit sizes, allowing them to work with files 2 GiB and larger. When the _FILE_OFFSET_BITS macro is defined as 64, the 64-bit functions are available as the original names.

Data structure

The metadata structure is defined in the header. The following shows the base fields, but an implementation is free to include additional fields:

struct stat ;

POSIX.1 does not require st_rdev, st_blocks and st_blksize members; these fields are defined as part of XSI option in the Single Unix Specification.
In older versions of POSIX.1 standard, the time-related fields were defined as st_atime, st_mtime and st_ctime, and were of type time_t. Since the 2008 version of the standard, these fields were renamed to st_atim, st_mtim and st_ctim, respectively, of type struct timespec, since this structure provides a higher resolution time unit. For the sake of compatibility, implementations can define the old names in terms of the tv_sec member of struct timespec. For example, st_atime can be defined as st_atim.tv_sec.
Fields include:st_dev – identifier of device containing filest_ino – inode numberst_mode – a bit field containing file access modes and special file type; see Unix permissionsst_nlink – reference count of hard linksst_uid – user identifier of ownerst_gid – group identifier of ownerst_rdev – device identifier st_size – total file size, in bytesst_atime – time of last accessst_mtime – time of last modificationst_ctime – time of last status changest_blksize – preferred block size for file system I/O, which can depend upon both the system and the type of file systemst_blocks – number of blocks allocated in multiples of DEV_BSIZE.

Example

The following C program reports metadata about each file passed via the command-line using to query the system for the information.

include
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int main