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Objective:

$ ls -l
total 42
drwx--xr-x 2 login wheel XX	Jun 1 20:47 test0
-rwx--xr-- 1 login wheel 4	Jun 1 21:46 test1
dr-x---r-- 2 login wheel XX	Jun 1 22:45 test2
-r-----r-- 2 login wheel 1	Jun 1 23:44 test3
-rw-r----x 1 login wheel 2	Jun 1 23:43 test4
-r-----r-- 2 login wheel 1	Jun 1 23:44 test5
lrwxr-xr-x 1 login wheel 5	Jun 1 22:20 test6 -> test0
$

Command ls -l output explanation

-rwxrw-r--    10    root   root 2048    Jan 13 07:11 afile.exe
?UUUGGGOOOS   00  UUUUUU GGGGGG ####    └─ date stamp and file name are obvious ;-)
↑ ↑  ↑  ↑ ↑    ↑      ↑      ↑    ↑
│ │  │  │ │    │      │      │    └─── File Size
│ │  │  │ │    │      │      └──────── Group Name (for example, Users, Administrators, etc)
│ │  │  │ │    │      └─────────────── Owner Acct
│ │  │  │ │    └────────────────────── Link count (what constitutes a "link" here varies)
│ │  │  │ └─────────────────────────── Alternative Access (blank means none defined, anything else varies)
│ └──┴──┴───────────────────────────── Read, Write and Special access modes for [U]ser, [G]roup, and [O]thers (everyone else)
└───────────────────────────────────── File type flag -

The permissions (mode) flags (UUUGGGOOO) are three sets of three chars, where the first set is "User" (i.e., Owner), the second set is "Group" and the third set is "Others" (i.e., everyone else; anyone who is neither Owner nor Group).

How to create all that we need

  • Remember that we use touch and mkdir to create files and folders respectively.

But now to the new part: we need to create a soft link for the folder test0

That is what the symbol -> means.

And if we pay attention to detail we notice that test5 is a hard link** of the file test3

We determine that due to the link count** size on both files plus the fact that they share the same date-stamp

And as a review of the difference between hard** and soft** links we can review this image:

Here is how we get to that picture:

  1. Create a name myfile.txt in the file system that points to a new inode (which contains the metadata for the file and points to the blocks of data that contain its contents, i.e. the text "Hello, World!": $ echo 'Hello, World!' > myfile.txt
  2. Create a hard link my-hard-link to the file myfile.txt, which means "create a file that should point to the same inode that myfile.txt points to": ln myfile.txt my-hard-link
  3. Create a soft link my-soft-link to the file myfile.txt, which means "create a file that should point to the file myfile.txt": ln -s myfile.txt my-soft-link Look what will now happen if myfile.txt is deleted (or moved): my-hard-link still points to the same contents, and is thus unaffected, whereas my-soft-link now points to nothing. Is up to future tasks to evaluate the pros/cons of each.

Changing the timestamp of a symlink

We just need to add the [OPTION] -h to touch

touch -h -a -m -t 201806012220.00 test6

Use man touch for more info.

Change the FILE SIZE + timestamp + permissions

But is better to leave it to the end, and for now focus on how to create all the folders and files accordingly with the requirements and come back to it latter.

How do file permissions apply to symlinks?

It depends on how you call chmod and the platform you are running on. For example, on a Linux system, man chmod says this:

chmod never changes the permissions of symbolic links; the chmod system call cannot change their permissions. This is not a problem since the permissions of symbolic links are never used. However, for each symbolic link listed on the command line, chmod changes the permissions of the pointed-to file. In contrast, chmod ignores symbolic links encountered during recursive directory traversals.

However, on a Mac, chmod can be used to modify the permissions of a symbolic link using options such as this (from man chmod):

-h If the file is a symbolic link, change the mode of the link itself rather than the file that the link points to.