Output from
ls -la Command
picard@spnode15$
ls -la
total 1600
drwx---s-x 11
picard STAFF 1536 Jun 26 14:49
.
dr-xr-sr-x1300 bin
bin 20480 Jun 26 12:06
..
-
rw------- 1
picard STAFF 948 Jun 06 09:46
.addressbook
-
rw------- 1
picard STAFF 3368 Jun 06 09:46
.addressbook.lu
-
rw------- 1
picard STAFF 193 Apr 02 10:06
.article
-
rw------- 1
picard STAFF 1035 May 20 12:30
.bash_history
drwx---S
-- 2
picard STAFF 512 Jun 23 13:56
.mailpgp
-
rw------- 1
picard STAFF 128654 Jun 10 19:19
.newsrc
drwx------ 4
picard STAFF 512 May 29 07:01
.pgp
-
rw------- 1
picard STAFF 10196 Jun 26 14:33
.pinerc
-
rwxr-xr-x 1
picard STAFF 1047 May 27 14:15
.plan
-
rw------- 1
picard STAFF 35 Jun 17 09:23
.profile
-
rw------- 1
picard STAFF 371 Sep 08 1995
.signature
-
rw------- 1
picard STAFF 81691 Jun 20 10:34 3dtree.jpg
-
rw------- 1
picard STAFF 31156 Jan 03 10:19
HTMLBgnrGuide.txt
drwx---s-x 2
picard STAFF 512 Apr 01 13:26 News
-
rw------- 1
picard STAFF 11760 Jul 23 1995 TUTORIAL
-
rw------- 1
picard STAFF 234 Feb 02 08:18
baen.txt
drwx---s-x 2
picard STAFF 512 Mar 12 06:57 bin
-
rw------- 1
picard STAFF 71 Jul 31 1995 calendar
-
rw------- 1
picard STAFF 338912
May 02 1995 command
.memos
-
rw------- 1
picard STAFF 747 Jun 24 13:12 dead
.letter
-
rw------- 1
picard STAFF 10506 Jun 01 12:42 info
.listserv
-
rw------- 1
picard STAFF 698675 Nov 01 1995
jim.kirk
.letters
-
rw------- 1
picard STAFF 122 Jun 24 13:28 junk
drwx------ 2
picard STAFF 1536 Jun 25 12:40 mail
-
rw-
r----- 1
picard STAFF 1397 May 28 12:50
mj.ultra
drwx---s-x 2
picard STAFF 512 May 26 21:09 pine
-
rw------- 1
picard STAFF 1716 Jul 23 1995 print.txt
drwxr-sr-x 6
picard STAFF 1024 Mar 27 10:54
public_html
drwx---s-x 3
picard STAFF 512 Mar 31 07:24
rexx
drwx---s-x 2
picard STAFF 512 Aug 08 1995 temp
-
rwx--x
--x 1
picard STAFF 368 May 28 14:10
unpgp
picard@spnode15$
Let's look at this
listing, and see what it tells us. At first glance, the left-most column looks like utter nonsense;
drwxr--blah-blah-blah. What's going on here?
File Type. The first position/character in this column describes what type of entry each horizontal line represents. The first character will usually be
either a - or a d. Symbols in the first (left most) position on the line represent:
-
= Regular File
d
= Directory
You can tell, just by looking at the output from
ls -
l which entries are files and which are directories.
Permissions. The rest of the first column (after the
- or d)
indicates access permissions which have
been set either explicitly, by you, using the
chmod command (which we'll look at later) or automatically, by the system, when the file (or directory)
was created. We'll discuss this part of the listing in more detail when we get to the
chmod command, which deals with setting file access permissions.
Directory Entries (and Hard-Link Count). The next column (immediately to the right of the access permissions) is a number which tells how many directory entries are under that item. For a regular file, this will typically be 1. For a directory, this will always be at least 2. The reason for this is that every directory always contains pointers to both itself, and its parent directory. You can see these two entries as the first two items in our example listing in Figure 12: the entries for
. and
.. (i.e. one period, and two periods). The single period
( .
), is the pointer to the current directory
--the directory
that you are "in" right now. Two periods
( ..
), point to the parent directory
--the directory which contains the current directory. You can use these as convenient nicknames/shortcuts in some commands, when you want to describe a relative
pathname.
Owner. The next column to the right displays the
userid of the owner of this file or directory. In our listing, most of the files
are owned by our hypothetical user,
picard. When you create files and directories, you will be their owner, and your
userid will show here, in place of
picard.
Group. The next column (mostly "STAFF" in our example) shows the name of the user group
which is connected with this entry. Each
userid is a member of one or more groups, and
access permissions may be set which determine what sort of access other members of the same group have to the file or directory named. Again, more on that when we get to the
chmod command.
Size. The next column shows the file size in bytes (characters).
Date/Time. The next 3 columns show the date and time the file was last
modified.
File Name. Finally, we have the file name. As discussed earlier, UNIX is very accommodating
with regard to the length of
file names.
However there are
some qualifications:
File names cannot (usually) contain blank spaces, or the characters /, *, or
?. This is because / is used to separate levels of a
pathname, * is a "wildcard" character which
is expanded by the system to mean "
any number of any characters," and
? is a wildcard representing "any single character." MS-DOS users in particular should recognize these "wildcard" characters.
http://docweb.cns.ufl.edu/docs/d0107/ar07s04.html
Most file systems that support hard links use reference counting.
An integer value is stored with each physical data section. This integer represents the total number of links that have
been created to point to the data. When a new link
is created, this value
is increased by one. When a link
is removed, the value
is decreased by one. If the link count becomes zero, the operating system usually automatically
deallocates the data space of the file if no process has the file opened for access. The maintenance of this value assists users in preventing data loss. This is a simple method for the file system to track the use of
a given area of storage, as zero values
indicate free space and nonzero values
indicate used space.
On POSIX-compliant operating systems, such as
many Unix-variants, the reference count for a file or directory
is returned by the
stat() or
fstat() system calls in the
st_nlink field of
struct stat.
- Link count: File vs Directory
One
of the results of the
ls -
l command is the link count.
1. What is the link count of a file?
The link count of a file tells the total number of links a file has
.the number of hard-links a file has.
The soft-link is not part of the link count since the soft-link's
inode number
is different from the original file.
2. How to find the link count of a file or directory?
any new file created will have a link count 1.
By default, a file will have a link count of 1
$ touch test.c
$ ln test.c test-
hardlink.c
$
ls -
lai
total 8
3145743
drwxrwxr-x 2 vagrant
vagrant 4096 Mar 31 11:44
.
3145730
drwxr-xr-x 6 vagrant
vagrant 4096 Mar 31 11:44
..
3145744 -
rw-
rw-
r-- 2 vagrant
vagrant 0 Mar 31 11:44 test.c
3145744 -
rw-
rw-
r-- 2 vagrant
vagrant 0 Mar 31 11:44 test-
hardlink.c
$ ln -s test.c test-
softlink.c
$
ls -
lai
total 8
3145743
drwxrwxr-x 2 vagrant
vagrant 4096 Mar 31 11:45
.
3145730
drwxr-xr-x 6 vagrant
vagrant 4096 Mar 31 11:44
..
3145744 -
rw-
rw-
r-- 2 vagrant
vagrant 0 Mar 31 11:44 test.c
3145744 -
rw-
rw-
r-- 2 vagrant
vagrant 0 Mar 31 11:44 test-
hardlink.c
3145745
lrwxrwxrwx 1 vagrant
vagrant 6 Mar 31 11:45 test-
softlink.c -> test.c
3. Does the link count decrease whenever the hard-link
is deleted?
When the hard link file
is moved or deleted, the link count of the original file gets reduced.
$
rm test-
hardlink.c
$
ls -
lai
total 8
3145743
drwxrwxr-x 2 vagrant
vagrant 4096 Mar 31 11:47
.
3145730
drwxr-xr-x 6 vagrant
vagrant 4096 Mar 31 11:44
..
3145744 -
rw-
rw-
r-- 1 vagrant
vagrant 0 Mar 31 11:44 test.c
3145745
lrwxrwxrwx 1 vagrant
vagrant 6 Mar 31 11:45 test-
softlink.c -> test.c
4. When does the link count of a directory change?
A directory "
xyz" is created and the default link count of any directory is 2. The extra count is because for every directory created, a link gets created in the parent directory to point to this new directory.
link count of a directory minus 2 gives you the total number of sub-directories present in the directory.
$
mkdir xyz
$
ls -
ld xyz/
drwxrwxr-x 2 vagrant
vagrant 4096 Mar 31 11:50
xyz/
$
mkdir -
p xyz/
abc
$
mkdir -
p xyz/
efg
$
ls -
ldia xyz
3145746
drwxrwxr-x 4 vagrant
vagrant 4096 Mar 31 11:51
xyz
http://www.theunixschool.com/2012/10/link-count-file-vs-directory.html
- Q1: The Unix inode structure contains a reference count. What is the reference count for? Why can't we just remove the inode without checking the reference count when a file is deleted?
Inodes contain a reference count
due to hard links. The reference count is equal to the number of directory entries that reference the
inode. For hard-linked files, multiple directory entries reference a single
inode. The
inode must not be removed until
no directory entries are left (ie, the reference count is 0) to ensure that the filesystem remains consistent.
- On a storage device, a file or directory is contained in a collection of blocks
Information about a file is contained in an
inode, which records information such as the owner, when the file was last accessed, how large it is,
whether it is a directory or not, and who can read from or write to it. The
inode number is also known as the file serial number and is unique within a particular filesystem
https://developer.ibm.com/tutorials/l-lpic1-104-6/
