This weeks lecture was a continuation of ‘Operating System II: File Management”. Most of the concepts covered in this weeks lecture I had looked at in last weeks review.
Some of the new points introduced were:
- When a file is accessed it has four id’s (I assume an example is real and sudo):
- a real user id
- an effective user id
- a real group id
- an effective group id
- Standard Input, Output, Error – Every time a shell is started. 3 files are opened automatically:
- stdin, (keyboard), 0
- stdout, (screen), 1
- sterr, (screen), 2
- Example of how inode numbers and logical directory structures work.
- How rwx Permissions work with directories: (Pearl of the Week)
- Read- Processes can list names and subdirectories within directory
- Write- Processes can alter the directory (create and remove files). To modify files write permission must be applied to the file.
- Excecute- Allows the user to cd into the directory. To open a file or excerpter a program a user must have execute permission on all directories leading to the files absolute path name.
- Hard and Soft(Symbolic) Links
- Locks (not covered in detail yet)
Pearl of the week: vi/vim text editor
$ vi myfile $ vim myfile
In the tut we worked with vi/vim text editor which is a tool I had struggled with before and had never bothered to read the tutorials on.
It turns out that it is a damn good editor as it is very very quick and easy once one becomes even moderately sufficient (2-3 hr tutorial). One of the primary advantages is that it runs within a command prompt environment so can be used via SSH with ease.
Some of the handy commands learnt in the tutorial are:
- i -> insert mode
- : -> comand mode
- esc -> back to normal mode
- CTRL + G -> End of the doc
- /prase -> find phrase
- n -> next phrase down
- N -> next phrase up
- :%s/word1/word2/gc -> replace all word1 with word2, gc adds confirmation for each occurance
- u -> undo
- d -> delete
- put -> put was what just deleted
- v -> visual select
- w -> word (dw -> delete word)
- $ -> end of line (d$ delete from cursor to end of line)
- :set tabstop=2 -> set tab distance to 2
- :set number -> show line numbers
- :set nonumber -> hide line numbers
- :1,4d -> delete lines 1,2,3,4
There are a great deal many useful examples of these which i shall add in as I use them.