Unix Operating system

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Unix Operating system

• You need to use secure telnet application to
  connect or login to a remote computer/machine
  and use i5.nyu.edu
• / points to a top directory (root)
• Pathname points to a specific file or directory
• /home/s/sao1
• Absolute path starts from the root directory
• /home/s/sao1
• Relative pathname points to
• a file or directory relative to your working
  directory
• (navigate up or down based on the current working
  directory you are in)
• cd .. Going back one level (up one level)
• cd ../.. Two levels up

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Summary of Unix Commands used in class

• Ls lists a directory of your files
• ls -l lists a directory with more information
  about the files
• ls -a lists a directory including the hidden
  files
• chmod modifies the permissions on a directory
• mkdir ltdirectory namegt creates a new directory
  (e.g. mkdir pictures creates a directory
  called "pictures")
• rmdir ltdirectory namegt removes an empty directory
  (e.g. rmdir pictures removes a directory called
  "pictures" as long as that directory is empty)
• cp ltcurrent filenamegt ltnew file namegt copy (e.g.
  cp cats1.jpg cats2.jpg makes a copy of the
  picture "cats1.jpg" and calls it "cats2.jpg")
• rm ltfilenamegt remove (or delete) a file (e.g. rm
  cats1.jpg deletes the file "cats1.jpg")
• cd ltdirectory namegt change directory
• Cd .. change directory up one level to the
  parent directory
• man This is the on-line Unix help documentation
  (as in "manual").
• Type "man" the command (e.g. "man ls") for a
  detailed explanation of the command.

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File and directory permission in UNIX

• R read permissions, you can look at a files
  content
• W write permissions, you can change or delete
  file or content
• X execute permissions, you can rum files as a
  program
• Lets look at permissions more closely on the next
  slide!

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File and directory permission in UNIX
Permissions Decimal Binary --- 0 000 ( all
bits off- no access) --x 1 001 ( only first
bit on- execute ) -w- 2 010 (Only second bit
on- write) -wx 3 011 (first and second bits
on- you can write execute) R-- 4 100 (third
bit is on- read) R-x 5 101 (third and first
bits on- read execute Rw- 6 110 (third and
second bits on- read and write) Rwx 7 111 (all
bits on- read, write and execute) Examples Chmod
755 public_html (rwx r-x r-x what
permissions?) Chmod 644 index.html (rw- r-- r--
what permissions?)
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File permission in UNIX

• To set permissions for the web
• Chmod 755 filename
• You can issue ls l to find out file permissions
• - rwx r-x r-x sana.jpg
• Image file for the web was set to 755
• Directory permissions
• drwx r-x r-x images