STAT

Section: System Calls (2)
Updated: October 25, 1987
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NAME

stat, lstat, fstat - get file status

SYNOPSIS

#include <sys/types.h>
#include <sys/stat.h>

stat(path, buf)
char *path;
struct stat *buf;

lstat(path, buf)
char *path;
struct stat *buf;

fstat(fd, buf)
int fd;
struct stat *buf;

DESCRIPTION

Stat obtains information about the file path. Read, write or execute permission of the named file is not required, but all directories listed in the path name leading to the file must be reachable.

Lstat is like stat except in the case where the named file is a symbolic link, in which case lstat returns information about the link, while stat returns information about the file the link references.

Fstat obtains the same information about an open file referenced by the argument descriptor, such as would be obtained by an open call.

Buf is a pointer to a stat structure into which information is placed concerning the file. The contents of the structure pointed to by buf

     struct stat {
          dev_t  st_dev;      /* device inode resides on */
          ino_t  st_ino;      /* this inode's number */
          u_short             st_mode;/* protection */
          short  st_nlink;    /* number or hard links to the file */
          uid_t  st_uid;      /* user-id of owner */
          gid_t  st_gid;      /* group-id of owner */
          dev_t  st_rdev;     /* the device type, for inode that is device */
          off_t  st_size;     /* total size of file */
          time_t st_atime;    /* file last access time */
          int    st_spare1;
          time_t st_mtime;    /* file last modify time */
          int    st_spare2;
          time_t st_ctime;    /* file last status change time */
          int    st_spare3;
          long   st_blksize;  /* optimal blocksize for file system i/o ops */
          long   st_blocks;   /* actual number of blocks allocated */
          long   st_serverID; /* Sprite ID of server holding inode */
          long   st_version;  /* Version number for file */
          long   st_userType; /* User-settable attribute word */
          long   st_devServerID;/* For devices, Sprite ID of device's machine */
    };

st_atime: Time when file data was last accessed. Changed by the following system calls: mknod(2), utimes(2), and read(2). For directories, the access time is changed each time a file name lookup passes through the directory.
st_mtime: Time when data was last modified. It is not set by changes of owner, group, link count, or mode. Changed by the following system calls: mknod(2), utimes(2), write(2).
st_ctime: Time when file status was last changed. It is set both both by writing and changing the i-node. Changed by the following system calls: chmod(2) chown(2), link(2), mknod(2), rename(2), unlink(2), utimes(2), write(2).
st_version: Version number for the file. It is incremented each time the file is opened for writing.

The status information word st_mode has bits:

#define S_IFMT  0170000  /* type of file */
#define    S_IFDIR       0040000/* directory */
#define    S_IFCHR       0020000/* character special */
#define    S_IFBLK       0060000/* block special */
#define    S_IFREG       0100000/* regular */
#define    S_IFLNK       0120000/* symbolic link */
#define    S_IFSOCK      0140000/* socket */
#define    S_IFPDEV      0150000/* pseudo-device */
#define    S_IFRLNK      0160000/* remote link */
#define S_ISUID 0004000  /* set user id on execution */
#define S_ISGID 0002000  /* set group id on execution */
#define S_IREAD 0000400  /* read permission, owner */
#define S_IWRITE         0000200/* write permission, owner */
#define S_IEXEC 0000100  /* execute/search permission, owner */

The mode bits 0000070 and 0000007 encode group and others permissions (see chmod(2)).

RETURN VALUE

Upon successful completion a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS

Stat and lstat will fail if one or more of the following are true:

[ENOTDIR]: A component of the path prefix is not a directory.
[EINVAL]: The pathname contains a character with the high-order bit set.
[ENAMETOOLONG]: A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
[ENOENT]: The named file does not exist.
[EACCES]: Search permission is denied for a component of the path prefix.
[ELOOP]: Too many symbolic links were encountered in translating the pathname.
[EFAULT]: Buf or name points to an invalid address.
[EIO]: An I/O error occurred while reading from or writing to the file system.

Fstat will fail if one or both of the following are true:

[EBADF]: Fildes is not a valid open file descriptor.
[EFAULT]: Buf points to an invalid address.
[EIO]: An I/O error occurred while reading from or writing to the file system.

CAVEAT

The fields in the stat structure currently marked st_spare1, st_spare2, and st_spare3 are present in preparation for inode time stamps expanding to 64 bits. This, however, can break certain programs that depend on the time stamps being contiguous (in calls to utimes(2)).

BUGS

Applying fstat to a socket (and thus to a pipe) returns a zero'd buffer, except for the blocksize field, and a unique device and inode number.

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Time: 04:51:42 GMT, January 31, 2023