stat(2) stat(2) st_ctime stat, fstat, lstat − get file status mode, etc.).

stat(2) stat(2) st_ctime stat, fstat, lstat − get file status mode, etc.).
stat(2)
stat(2)
stat(2)
stat(2)
The field st_ctime is changed by writing or by setting inode information (i.e., owner, group, link count,
mode, etc.).
NAME
stat, fstat, lstat − get file status
The following POSIX macros are defined to check the file type:
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
int stat(const char * file_name, struct stat *buf );
int fstat(int filedes, struct stat *buf );
int lstat(const char * file_name, 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.
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:
stat stats the file pointed to by file_name and fills in buf .
lstat is identical to stat, except in the case of a symbolic link, where the link itself is stat-ed, not the file that
it refers to.
fstat is identical to stat, only the open file pointed to by filedes (as returned by open(2)) is stat-ed in place
of file_name.
They all return a stat structure, which contains the following fields:
struct stat {
dev_t
ino_t
mode_t
nlink_t
uid_t
gid_t
dev_t
off_t
blksize_t
blkcnt_t
time_t
time_t
time_t
};
S_ISREG(m)
st_dev;
/* device */
st_ino; /* inode */
st_mode; /* protection */
st_nlink; /* number of hard links */
st_uid; /* user ID of owner */
st_gid; /* group ID of owner */
st_rdev; /* device type (if inode device) */
st_size; /* total size, in bytes */
st_blksize; /* blocksize for filesystem I/O */
st_blocks; /* number of blocks allocated */
st_atime; /* time of last access */
st_mtime; /* time of last modification */
st_ctime; /* time of last status change */
S_IFMT
S_IFSOCK
S_IFLNK
S_IFREG
S_IFBLK
S_IFDIR
S_IFCHR
S_IFIFO
S_ISUID
S_ISGID
S_ISVTX
S_IRWXU
S_IRUSR
S_IWUSR
S_IXUSR
S_IRWXG
S_IRGRP
S_IWGRP
S_IXGRP
S_IRWXO
S_IROTH
S_IWOTH
S_IXOTH
0170000
0140000
0120000
0100000
0060000
0040000
0020000
0010000
0004000
0002000
0001000
00700
00400
00200
00100
00070
00040
00020
00010
00007
00004
00002
00001
bitmask for the file type bitfields
socket
symbolic link
regular file
block device
directory
character device
fifo
set UID bit
set GID bit (see below)
sticky bit (see below)
mask for file owner permissions
owner has read permission
owner has write permission
owner has execute permission
mask for group permissions
group has read permission
group has write permission
group has execute permission
mask for permissions for others (not in group)
others have read permission
others have write permisson
others have execute permission
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 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
group ID 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 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 "preferred" blocksize for efficient file system I/O.
(Writing to a file in smaller chunks may cause an inefficient read-modify-rewrite.)
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 a privileged process.
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.
RETURN VALUE
On success, zero is returned. On error, −1 is returned, and errno is set appropriately.
SEE ALSO
chmod(2), chown(2), readlink(2), utime(2), capabilities(7)
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.
SOSI-Klausur Manual-Auszug
2006-06-22
1
SOSI-Klausur Manual-Auszug
2006-06-22
2
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