fstat(2) - Waikato Linux Users Group

NAME

fstat - get file status

SYNOPSIS

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

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

DESCRIPTION

These functions return information about the specified file. You do not need any access rights to the file to get this information but you need search rights to all directories named in the path leading to the file.

fstat(2) takes the metadata of the file opened with filedes and places that information in the structure ''buf' which contains the following elements: struct stat {

dev_t st_dev; /* device / ino_t st_ino; / inode / mode_t st_mode; / protection / nlink_t st_nlink; / number of hard links / uid_t st_uid; / user ID of owner / gid_t st_gid; / group ID of owner / dev_t st_rdev; / device type (if inode device) / off_t st_size; / total size, in bytes / unsigned long st_blksize; / blocksize for filesystem I/O / unsigned long st_blocks; / number of blocks allocated / time_t st_atime; / time of last access / time_t st_mtime; / time of last modification / time_t st_ctime; / time of last change */ };

The value st_size gives the size of the file (if it is a regular file or a symlink) in bytes. The size of a symlink is the length of the pathname it contains, without trailing NUL.

The value st_blocks gives the size of the file in 512-byte blocks. (This may be smaller than st_size/512 e.g. when the file has holes.) The value st_blksize gives the ''

Not all of the Linux filesystems implement all of the time fields. Some file system types allow mounting in such a way that file accesses do not cause an update of the st_atime field. (See `noatime' in mount(8).)

The field st_atime is changed by file accesses, e.g. by execve(2), mknod(2), pipe(2), utime(2) and read(2) (of more than zero bytes). Other routines, like mmap(2), may or may not update st_atime.

The field st_mtime is changed by file modifications, e.g. by mknod(2), truncate(2), utime(2) and write(2) (of more than zero bytes). Moreover, st_mtime of a directory is changed by the creation or deletion of files in that directory. The st_mtime field is not changed for changes in owner, group, hard link count, or mode.

The field st_ctime is changed by writing or by setting inode information (i.e., owner, group, link count, mode, etc.).

The following POSIX macros are defined to check the file type:

S_ISREG(m): is it a regular file?
S_ISDIR(m): directory?
S_ISCHR(m): character device?
S_ISBLK(m): block device?
S_ISFIFO(m): fifo?
S_ISLNK(m): symbolic link? (Not in POSIX.1-1996.)
S_ISSOCK(m): socket? (Not in POSIX.1-1996.)

The following flags are defined for the st_mode field:

The set GID bit (S_ISGID) has several special uses: For a directory it indicates that BSD semantics is to be used for that directory: files created there inherit their group ID from the directory, not from the effective gid of the creating process, and directories created there will also get the S_ISGID bit set. For a file that does not have the group execution bit (S_IXGRP) set, it indicates mandatory file/record locking.

The `sticky' bit (S_ISVTX) on a directory means that a file in that directory can be renamed or deleted only by the owner of the file, by the owner of the directory, and by root.

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

EBADF: filedes is bad.
ENOENT: A component of the path file_name does not exist, or the path is an empty string.
ENOTDIR: A component of the path is not a directory.
ELOOP: Too many symbolic links encountered while traversing the path.
EFAULT: Bad address.
EACCES: Permission denied.
ENOMEM: Out of memory (i.e. kernel memory).

CONFORMING TO

The fstat(2) calls conform to SVr4, SVID, POSIX, X/OPEN, BSD 4.3. SVr4 documents additional fstat(2) error conditions EINTR, ENOLINK, and EOVERFLOW.

Use of the st_blocks and st_blksize fields may be less portable. (They were introduced in BSD. Are not specified by POSIX. The interpretation differs between systems, and possibly on a single system when NFS mounts are involved.)

POSIX does not describe the S_IFMT, S_IFSOCK, S_IFLNK, S_IFREG, S_IFBLK, S_IFDIR, S_IFCHR, S_IFIFO, S_ISVTX bits, but instead demands the use of the macros S_ISDIR(), etc. The S_ISLNK and S_ISSOCK macros are not in POSIX.1-1996, but both will be in the next POSIX standard; the former is from SVID 4v2, the latter from SUSv2.

Unix V7 (and later systems) had S_IREAD, S_IWRITE, S_IEXEC, where POSIX prescribes the synonyms S_IRUSR, S_IWUSR, S_IXUSR.

OTHER SYSTEMS

Values that have been (or are) in use on various systems:

|^hex|^name|^ls|^octal|^description |f000|S_IFMT| |170000|mask for file type |0000|| |000000|SCO out-of-service inode, BSD unknown type, SVID-v2 and XPG2 have both 0 and 0100000 for ordinary file |1000|S_IFIFO|p (pipe symbol)|010000|fifo (named pipe) |2000|S_IFCHR|c|020000|character special (V7) |3000|S_IFMPC| |030000|multiplexed character special (V7) |4000|S_IFDIR|d/|040000|directory (V7) |5000|S_IFNAM| |050000|XENIX named special file with two subtypes, distinguished by st_rdev values 1, 2: |0001|S_INSEM|s|000001|XENIX semaphore subtype of IFNAM |0002|S_INSHD|m|000002|XENIX shared data subtype of IFNAM |6000|S_IFBLK|b|060000|block special (V7) |7000|S_IFMPB| |070000|multiplexed block special (V7) |8000|S_IFREG|-|100000|regular (V7) |9000|S_IFCMP| |110000|VxFS compressed |9000|S_IFNWK|n|110000|network special (HP-UX) |a000|S_IFLNK|l@|120000|symbolic link (BSD) |b000|S_IFSHAD| |130000|Solaris shadow inode for ACL (not seen by userspace) |c000|S_IFSOCK|s=|140000|socket (BSD; also "S_IFSOC" on VxFS) |d000|S_IFDOOR|D>|150000|Solaris door |e000|S_IFWHT|w%|160000|BSD whiteout (not used for inode) |0200|S_ISVTX| |001000|`sticky bit': save swapped text even after use (V7), reserved (SVID-v2), On non-directories: don't cache this file (SunOS), On directories: restricted deletion flag (SVID-v4.2) |0400|S_ISGID| |002000|set group ID on execution (V7), for directories: use BSD semantics for propagation of gid |0400|S_ENFMT| |002000|SysV file locking enforcement (shared w/ S_ISGID) |0800|S_ISUID| |004000|set user ID on execution (V7) |0800|S_CDF| |004000|directory is a context dependent file (HP-UX)

A sticky command appeared in Version 32V AT

EXAMPLE

/* fstat(2)'s a file, and displays the results

*

/

include <sys/stat.h> /* for struct stat, fstat(2), S_* constants */

include <sys/types.h>/* for mode_t, uid_t, etc... */

include <errno.h> /* for errno */

include <fcntl.h> /* for open(2), O_* */

include <pwd.h> /* for getpwuid(3) */

include <string.h> /* for strerror(3) */

include <stdio.h> /* for printf(3) etc */

include <time.h> /* for asctime(3) */

include <unistd.h> /* for close(2) */

int do_stat(char *filename) {

int fd; struct stat statbuf;

fd = open(filename,O_RDONLY);

if (fd == -1) {

printf("fstat: open(\"%s\",O_RDONLY): %s (%i)",

filename, strerror(errno), errno);

return 1;

}

if (fstat(fd,&statbuf) == -1) {

printf("fstat: fstat: %s (%i)",

strerror(errno), errno);

return 1;

}

if (S_ISREG(statbuf.st_mode)) printf("Regular file"); else if (S_ISDIR(statbuf.st_mode)) printf("Directory"); else if (S_ISCHR(statbuf.st_mode)) printf("Character Device"); else if (S_ISBLK(statbuf.st_mode)) printf("Block Device"); else if (S_ISFIFO(statbuf.st_mode)) printf("Fifo"); else if (S_ISLNK(statbuf.st_mode)) printf("Symbolic Link"); else if (S_ISSOCK(statbuf.st_mode)) printf("Socket"); printf(": \"%s\"\n",filename); printf("Size: %-20i Blocks: %-10i Block Size: %-10i\n",

(int)statbuf.st_size, (int)statbuf.st_blocks, (int)statbuf.st_blksize);

printf("Device: 0x%06llx (%7llu) Inode: %-10li Links: %i\n",

statbuf.st_dev, statbuf.st_dev, statbuf.st_ino, statbuf.st_nlink);

printf("Access: %c%c%c%c%c%c%c%c%c (0%-5o) User ID: %i(%s) Group ID: %i(%s)\n",

statbuf.st_mode & S_IRUSR ? 'r' : '-', statbuf.st_mode & S_IWUSR ? 'w' : '-', statbuf.st_mode & S_ISUID ? (

statbuf.st_mode & S_IXUSR ? 's' : 'S' ) : ( statbuf.st_mode & S_IXUSR ? 'x' : '-' ),

statbuf.st_mode & S_IRGRP ? 'r' : '-', statbuf.st_mode & S_IWGRP ? 'w' : '-', statbuf.st_mode & S_ISGID ? (

statbuf.st_mode & S_IXGRP ? 's' : 'S' ) : ( statbuf.st_mode & S_IXGRP ? 'x' : '-' ),

statbuf.st_mode & S_IROTH ? 'r' : '-', statbuf.st_mode & S_IWOTH ? 'w' : '-', statbuf.st_mode & S_ISVTX ? (

statbuf.st_mode & S_IXGRP ? 't' : 'T' ) : ( statbuf.st_mode & S_IXGRP ? 'x' : '-' ),

statbuf.st_mode, statbuf.st_uid,getpwuid(statbuf.st_uid)->pw_name, statbuf.st_gid,getpwuid(statbuf.st_gid)->pw_name);

printf("Access Time: %s", ctime(&statbuf.st_atime)); printf("Modify Time: %s", ctime(&statbuf.st_mtime)); printf("Change Time: %s", ctime(&statbuf.st_ctime));

if (close(fd) == -1) {

printf("fstat: close(fd): %s (%i)",

strerror(errno), errno);

return 1;

}

return 0;

}

int main(int argc, char **argv) {

int i;

if (argc<2) {

printf("%s: too few arguments\n",argv[0?); printf("usage: %s filename...\n",argv[0?); return 1;

} for (i=1;i<argc;i++) {

do_stat(argv[i?);

} return 0;

}