CENG151 Lecture PointsWeek 1

Part I: Preliminary Steps

PUTTY TIPS

Choose a different font size & style

Port 22 means putty uses ssh. Leave this alone

Choose “System Colors”For black text, white background.

Turn off that annoying bell

Specify your login id & system

Define the settings you want, give it a name and Save for later

Select “Use Unicode line drawing code points so you can put emojis in your code

Download & install putty from: https://www.chiark.greenend.org.uk/~sgtatham/putty/

Use this to set a file to record your session

https://www.chiark.greenend.org.uk/~sgtatham/putty/

MAC TERMINALPREFERENCES

Choose a different font size & style

Turn off that annoying bell

Logging in from Mac Terminal (or connecting from one Unix system to another)

ssh yourid@location

ie: ssh n0123456789@apollo.humber.ca

mailto:yourid@location

DO THIS ONCE ONLY

The following sets up vim to use a resource file .vimrc

ln -sf ~king/.vimrc ~/.vimrc

ls -la ~ #Shows your home directory including hidden files

#You should see…

lrwxrwxrwx 1 user student 6 date .vimrc -> ~king/.vimrc

Part II: Navigating Unix’s Directory Tree

Standard Unix Directories/

/bin essential system binaries

/boot/dev -terminals, disks, devices, mice - /dev/pts/1 ....

/dev/tty - always a synonym for the current terminal/dev/null - watch for it

/etc - host specific system configuration files/home

/mnt mounted devices/opt - add on optional software/root/sbin - system binaries/tmp - temporary files/usr - NOT USER, unix systems resources

/usr/bin - most user commands/usr/include - standard C include files/usr/lib - libraries for programming and packages

/var - varying data files - account information, logs, system web pages

Unix Directory Commands

pwd #print working directory

cd name #change directory Also works with ~ $HOME

mkdir newDir #create a directory

rmdir oldDir #remove a directory (must be empty!)

ls –ld dirName #Show the properties of the directory, not its contentscd .. #move to the parent directorycd ../.. #move to the grandparent directory

cd /usr/bin #move to the absolute path location

cd ../include #move up a directory & down to include – relative path

cd - #switch to immediately previous directory

. & ..

Every directory has at least 2 files: . and ..

. represents the current directory

.. represents the parent of the current directory

Part III: Security/File Permissions

Security applies to 3 entities

This Photo by Unknown Author is licensed under CC BY-SA-NC

This Photo by Unknown Author is licensed under CC BY-SA

Users (you) Others

Groups

https://oldschool.runescape.wiki/w/Minnowhttps://creativecommons.org/licenses/by-nc-sa/3.0/https://commons.wikimedia.org/wiki/File:Crystal_Clear_kdm_user_female.svghttps://creativecommons.org/licenses/by-sa/3.0/

Files in Unix have 3 privileges which can be combined

ReadExecute/Navigable

Write

Navigable only applies to directorys

The ls -l command displays file permissions in symbolic form

- r w x r w - - - -

User (you) Group Others

The chmod command uses the symbols ugo + - = rwxto change file permissions. You can separate specifications by a comma, no spaces

chmod u=,a+rx,go-x,g+r file1 file2 file3

There are 8 possible combinations of r, w and x

rwx

000 0 - - -

001 1 - - x

010 2 - w -

011 3 - w x

100 4 r - -

101 5 r – x

110 6 r w -

111 7 r w x

chmod 0711 file1 file2 file3…

Permissions affect the visibility of your files and directories to others.

Browsers: The visibility of web pagesfinger: The visibility of the .plan and .project filesecho: The visibility of a terminal

Writing on someone else’s terminal:

Them: chmod g+w /dev/pts/7

You: echo “Hello, this is $USER” > /dev/pts/7

*Whenever you see “ “ or ‘ ‘ in an assignment or in documentation, do not cut and paste to Unix. These are “Microsoft Quotes” and not the same as

" " or ' ‘ which are ASCII values.

Access Control Lists

setfacl -m u::rwx,g::r,o:r,u:vgld0005:rw,g:sharks:r file1 file2 …

#Deleting an ACL permissionsetfacl -x g:shark file1

#Showing an ACL permissiongetfacl f1

Using an ACL permission the owner of file can grant or deny access to any individual or group. There is a limit of about 500 ACL entries to a file. If there is a need for

Part IV: Switching between systems

The ssh command can be used to log into another system.

This is what Mac and Linux users in this course use to connect to apollo and munro.

[king@apollo ~ ] ssh king@munro.humber.ca

king @ munro.humber.ca’s password:

-bash-3.2$

It may also work with your version of Windows 10 command line or PowerShell if has been

updated since May 2019.

ssh #secure shell command

mailto:king@munro.humber.ca

The ssh command can be used to run one or more commands on the remote machine or

on the same machine using a different account

Ssh king@apollo.humber.ca finger

ssh kingtest@apollo.humber.ca “uptime;date;who”

ssh target cmd

ssh target “cmd1; cmd2”

mailto:king@apollo.humber.camailto:kingtest@apollo.humber.ca

The scp command can be used to copy files between two different machines, even if you

are not currently logged on to either!

scp king@apollo.humber.ca:hello.c . #copy from apollo to the current dir

scp king@apollo.humber.a:hello.c helloX.c #copy to a new name

scp -p king@munro.humber.ca:report.doc kingtest@apollo.humber.ca:report.doc

scp #secure copy command

mailto:king@apollo.humber.ca:hello.cmailto:king@apollo.humber.a:hello.cmailto:king@minvera.humber.ca:report.doc

The su command lets you switch to a different account on the same machine:

su kingtest

password:

su #substitute user command

vim scp://user@apollo.humber.ca/someFile.txt

user@apollo.humber.ca password: (enter your password)

If you are already in vim you can use either the :e command or the :n command

:e scp://user@apollo.humber.ca/someFile.txt

:n scp://user@apollo.humber.ca/someFile.txt

:w and :wq will save the file that you loaded

:w scp://user@machine/otherName.txt

Using scp with vim to edit remote files

mailto:user@apollo.humber.ca

The newgrp command allows you to change your current group to any other group where

you happen to be a member. Most systems will prompt you for a group password. Our

systems don’t.

newgrp sharks

id

uid=551(king) gid=2331(sharks) groups=504(staff),2331(sharks),2332(minnows)

newgrp #switch to a different group

Part V: More Vim

Vimtutor

Section 3

Section 4

Section 6.1-6.4

Topic Moved to June 3-4

Part VI: Aliases to FilesHard Links and Symbolic Links

inodesThe -i flag of the ls command shows the inode of each file.

An inode is a unique number (per hard drive), handed out in sequence that represents a file.

A directory consists of a set of inodes and file names. That’s it!

2893824 file1

2893825 file2

2893826 file3

3182611 myReport.txt

17001428 Schedule.dat

.

.

.

.

.

.

Each inode # points to a location in the SuperBlock, a region of the disk drive where file properties such as atime, mtime and ctime and the file’s contents are kept, but not the file name:

2893824 file1

2893825 file2

2893826 file3

3182611 myReport.txt

17001428 Schedule.dat

.

.

.

.

.

.

SUPERBLOCK HEADER

Permissions

Size

link count

atime

mtime

Ownerid

Groupid

link to content File contents

3182611

Permissions

Size

link count

atime

mtime

ownerid

Groupid

link to content

2893824

File contentsPermissions

Size

link count

atime

mtime

ownerid

Groupid

link to content

2893825

File contents

mv Schedule.dat newSched.dat

The mv (move) command can rename a file or move it between directories. It does not copy the data, it renames the file and reuses the same inode#.

2893824 file1

2893825 file2

2893826 file3

3182611 myReport.txt

17001428 newSched.dat

.

.

.

.

.

.

ln file1 fileXYZln file1 dir2/anotherNameThe ln (link) command can rename a file or move it between directories. It does not copy the data, it renames the file and reuses the same inode#.The link count of the file will increase by 1. Only the inode# and the name are affected.

2893824 file1

2893825 file2

2893826 file3

3182611 myReport.txt

17001428 newSched.dat

2893824 fileXYZ

.

.

.

.

.

.

57282 hello.c

57888 Lab1.mak

2893824 anotherName

dir2

dir1

rm file1unlink fileThe rm (remove) and unlink commands remove a file and its inode from a directory and reduce the link count in the SuperBlock by 1. The data and the file properties arestill kept… and only removed from the system when the link count goes to zero.

2893825 file2

2893826 file3

3182611 myReport.txt

17001428 newSched.dat

2893824 fileXYZ

.

.

.

.

.

.

57282 hello.c

57888 Lab1.mak

2893824 anotherName

dir2

dir1

ln -s dir1/fileXYZ dir2/symLink1The hard link idea had one problem. People would move hard disks from system to system. You couldn’t guarantee that the inode #s would be unique between disks. Hard links don’t work across different devices.

The solution: create a 2nd technique: create a new file type called symbolic link. The content of this new file would be the name of the old file.

2893824 file1

2893825 file2

2893826 file3

3182611 myReport.txt

17001428 newSched.dat

2893824 fileXYZ

57282 hello.c

57888 Lab1.mak

2893824 anotherName

3100105 symlink2

Setting up .vimrc (vim resource control file) using a symbolic link

Enter the following command on apollo. This is a one time only requirement and will be explained in class. The spaces are exaggerated to make sure that you use them.

ln -sf ~king/.vimrc ~/.vimrc