update docker and unix commands, add unix permissions

docs/source/index.rst

@@ -69,6 +69,7 @@ The organization of this site is as following:
 
    reference/unix/mount-and-unmount
    reference/unix/unix-file-system
+   reference/unix/unix-permissions
 
 
 .. toctree::

docs/source/reference/commands/docker-commands.md

@@ -39,7 +39,7 @@ docker pull
 
 docker container ls --all -aq
 
-docker stat
+docker stat # show real time stat
 ```
 
 ## Run

docs/source/reference/commands/unix-and-linux-commands.md

@@ -1167,9 +1167,10 @@ The event reference (!) is mainly used in scripts?
     # PUT
     curl --upload-file [some_file] [URL]
 
+    # Get more details
+    curl -i # include response headers
     curl --verbose
-    curl -v
-
+    curl -v # abbr for verbose
     # record everything sends and receives
     curl --trace [dump_file_name]
     curl --trace-ascii [dump_file_name]
@@ -1708,6 +1709,37 @@ lpq -P [printer]
 lprm -P [printer] [Jobs-id\username]
 ```
 
+## Gpg Signature
+
+`gpg`
+
+```bash
+gpg --import [keyfile]
+gpg2 --keyserver [URL_to_key_server] --search-keys [sender]
+
+gpg --verify [sigfile] [file]
+
+gpg --full-generate-key # generate new key
+gpg --gen-revoke [KEYID] # generate revoke
+gpg --send-keys [KEYID] # publish your keys to internet
+
+gpg --list-secret-keys --keyid-format LONG
+```
+
+Use `gpg` with git
+
+```bash
+git config --global commit.gpgsign true     # turn on gpg sign
+git config --global user.signingkey [KEYID] # assign gpg key
+
+# windows gpg
+git config --global gpg.program "/c/GnuPG/bin/gpg.exe"
+git config --global gpg.program "C:\GnuPG\bin\gpg.exe"
+
+git commit --amend --no-edit -n -S          # sign the last commit, maybe need to force push later
+git rebase --exec 'git commit --amend --no-edit -n -S' -i [tag,hash] # another way to go?
+```
+
 ## Distrubution Specific
 
 ### Debian

docs/source/reference/unix/unix-permissions.md

@@ -0,0 +1,193 @@
+# Unix Permissions
+
+## Basic
+
+Permissions are a mechanism to restrict the access to resources.
+
+Each file has specific permissions, owner, and owner group.
+
+Each process is executed as a user. The process has the same privileges as the user does.
+
+Root user has no permission restrictions.
+
+## Categories
+
+There are 3 types of permissions:
+
+* Read (r)
+  * read the content of a file
+  * list the contents of a directory
+  * 2^2 = 4
+* Write (w)
+  * change the content of a file
+  * create or delete files in a directory
+  * 2^1 = 2
+* Execute (x)
+  * run a file as command
+  * access the content in a directory
+    * Directories without x cannot be 'opened' (check the content inside a directory)
+  * 2^0 = 1
+
+Usually permissions are encoded using octal numbers.
+For a number 'rwx', r is the 3rd bit, w is the 2nd bit, x is the 1st bit.
+
+Therefore 'rw-' is '110' and thus 6. Same thing for other encodings.
+
+## UGO
+
+There are 3 parts of permissions for the 9 permission bits:
+
+`User Group Other`
+
+* Owner of the file: User, the first 3 bits
+* Group of the file: Group, the middle 3 bits
+* Other users: Other, the last 3 bits
+
+There are also 3 special bits for a file.
+
+## Inspect Permissions
+
+```bash
+$ ls -l
+drwxr-xr-- 2 some-user some-group 208 Oct 1 13:50 some-directory
+# UGO | number of links | owner | group | size | time of last modification | name
+```
+
+```bash
+drwxr-xr--
+
+# d:    is directory
+# rwx : owner permission
+# r-x : group permission
+# r-- : other permission
+```
+
+## Modify Permission
+
+`chown`
+
+```bash
+chown some-user some-file
+chown -R some-user some-directory
+```
+
+Change the owner
+
+-R: recursively change all subdirectories and files
+
+`chgrp`
+
+Change the owner group
+
+Same usage as `chown`
+
+`chmod`
+
+```bash
+chmod <new_permission> <some_file>
+
+chmod u+rw ./a.out
+chmod g-x ./a.out
+chmod go+r ./a.out
+chmod a-x ./a.out
+chmod u+x ./a.sh
+
+chmod 660 ./a.out # rw-rw----
+chmod 775 ./a.out # rwxrwxr-x
+```
+
+Change the permissions
+
+## Default Permission
+
+There is something controlling the default permission for a new file created.
+
+`umask`
+
+Subtraction
+
+* Permission for a newly created file: 666 - `umask`
+* Permission for a newly created directory: 777 - `umask`
+
+Each user has a umask property
+
+There are 4 bits for umask. The first 3 bits are UGO and the last bit is special permission.
+
+umask value by default:
+
+* normal user
+  * 002
+  * 666 - 002 = 664
+  * rw-rw-r--
+* root
+  * 022
+  * 666 - 022 = 644
+  * rw-r--r--
+
+It's actually not subtraction but a bitwise XOR (?)
+
+```bash
+umask                   # inspect
+umask <new_umask_value> # set
+```
+
+## Special Permissions
+
+What about the 'extra' bit, or the 4th bit, of umask?
+
+The real permission in binary is 12bits. UGO uses 9 bits.
+The last 3 bits, namely the leading bit of umask, is the [special permission bit](https://docs.oracle.com/cd/E19683-01/816-4883/secfile-69/index.html).
+
+### suid
+
+Run the command with the access permissions of the owner, not the user executing this command.
+
+```bash
+$ ls -l /usr/bin/passwd
+-rwsr-xr-x 1 root root 53K May 16  2017 /usr/bin/passwd*
+```
+
+The 'x' bit of U becomes 's'.
+
+The user executing this command will potentially gain extra access.
+
+Usually, the file name will be colored and highlighted on a terminal with color support.
+
+```bash
+chmod u+s  xxx
+```
+
+### sgid
+
+Same as 'suid' but uses the permission of the group owner.
+
+The 'x' bit of G becomes 's'.
+
+Usually set for directories. It is commonly used to inherit the permissions of parent directory.
+
+```bash
+chmod g+s xxx
+```
+
+### Sticky Bit
+
+Users with write access to a directory can only delete the files owned by this user.
+They can not delete other files in this directory which are owned by other users.
+
+Used to protect a directory shared by multiple people. Usually within same group.
+
+Usually the directory name will be highlighted using blue color.
+
+```bash
+chmod o+t xxx
+```
+
+### Octal Numbers for Special Permissions
+
+suid = 4
+sgid = 2
+sticky = 1
+
+```bash
+chmod 4755 xxx
+```