File Systems (ch 4) IT244 - Introduction to Linux / Unix Instructor: Bo Sheng 1.

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File Systems (ch 4)

IT244 - Introduction to Linux / Unix Instructor: Bo Sheng

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Outline

• Filename and paths• Directory operations• Access permissions

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Filenames and Paths

• Absolute path name

– ls /home/it244/it244– ls /home/it244/it244/

/home/it244/it244/hello

Path Filename

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Filenames and Paths

• Absolute path name

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Filenames and Paths

• Absolute path name– ~ represents “home directory”

– ls ~ =ls /home/your username– cd ~– pwd

– ls ~it244 =ls /home/it244

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Filenames and Paths

• Relative path name

– cd /home/it244– ls it244

/home/it244/it244/hello

Path Filename

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Filenames and Paths

• Relative path name– . : Current directory– .. : Parent directory

– ls –la– ls .– ls ..– cd ..– cd ../..

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Filenames and Paths

• Relative path name

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Filenames and Paths

• Standard directories (Pg 95~98)

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Directory Operations

• Create a directory– mkdir book– ls -l– ls book– ls ./book– cd book– ls ../book

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• Delete a directory (when it’s empty)– cd ..– rmdir book

• Example– mkdir book– cd book– echo “this is a book” > book1– cd ..– rmdir book (not empty)

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• Example– rm book/book1– rmdir book

• Delete directories by rm– mkdir book– rm book– rm –r book (cautious)

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• Example– mkdir book– cd book– mkdir novel– cd ..– rmdir book

– cd book/novel– rmdir .

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• Copy and move files to directories– cd ../..– cp hello book– ls book

– mv welcome linux book– ls– ls book

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• Copy and move files to directories– mv book newbook

– mv newbook book– ls

– mkdir newbook– mv book newbook

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• Copy and move files to directories– mv newbook/book book– cp book newbook ???

– cp –r book newbook– ls newbook

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Access Permissions

• Three types of users– Owner– Group member– Others

• Three access permissions– Read– Write– Execute

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Access Permissions

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Access Permissions

• Change access permissions (chmod)– Symbolic arguments

• a (all), u (owner), g (group), o (others)• r (read), w (write), x (execute)• + / -

• chmod a+w book1• chmod go-rw book1

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Access Permissions

• Change access permissions (chmod)– Numeric arguments

r w x 1

2

3

4

5

6

7

-rw-r--r--644

-rwxr-xr-x755

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Access Permissions

• Change access permissions (chmod)– Numeric arguments

• chmod 644 book1• chmod 755 book1

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Access Permissions

• Example– Read permission

• chmod a-r hello• cat hello• chmod a+r hello• cat hello

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Access Permissions

• Example– Read permission

• chmod a-r book• ls book• ls book/book1• chmod a+r book

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Access Permissions

• Example– Write permission

• chmod a-w hello• echo hi>hello

• rm hello• chmod a+w hello• rm hello

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Access Permissions

• Example– Write permission

• cd book• chmod a-w .• chmod a+rw book1

• echo hi>book2 (create a file)• mv book1 book2 (rename a file)• rm book1 (delete a file)• chmod a+w .

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Access Permissions

• Example– Execute permission (directory)

• Determine if the files are searchable• chmod a-x book• ls book• ls book/book1

• cd book• chmod a+x book

Why?

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Access Permissions

• Execute permission on files– Binary and script

– cp /home/shengbo/it244/binary .– cp /home/shengbo/it244/script .

– ls –l (check the execute permission)– cat binary– cat script

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Access Permissions


– chmod a=x binary– ./binary

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Access Permissions


– chmod a=x script– ./script– chmod a=rx script

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Access Permissions

• Execute permission on files– Binary ( x )– Script ( rx )

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Access Control List

• ACL: fine-grained access control– getfacl and setfacl

• getfacl hello

• setfacl –m u:shengbo:rw- hello• getfacl hello

• setfacl –m u:shengbo:4 hello• getfacl hello

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Access Control List

• ACL: fine-grained access control– getfacl and setfacl

• setfacl –m u:shengbo:rw-,u:vijeth35:6 hello

• getfacl hello

• setfacl –x u:vijeth35 hello• getfacl hello

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Links

• Pointer to a file or directory

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Links

• Example– ls –l ~

– cd it244– pwd

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Links

• Example– ls –l ~

/

it244username

usernameit244

home courses

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Links

• Hard links and symbolic links– Hard links point to the actual data

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Links


– ln hello hello1– ls -l– ls –i hello hello1 (inode number)

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Links


– cat hello hello1– rm hello– cat hello1– ln VS. cp

– Hard links cannot point to directories

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Links

• Hard links and symbolic links– Symbolic (soft) links are shortcuts

Hard link Symbolic link

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Links


– ln –s hello hello2– ls -l– ls –i hello hello1 hello2

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Links


– cat hello hello1 hello2– rm hello– cat hello1– cat hello2– echo hi > hello– cat hello hello1 hello2

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Links

• Hard links and symbolic links– Remove links– rm hello1

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Summary

• More about file system and inode

Data blocks

inode

file1

File type

Size

Permissions

Block addr

…

Inode number

Inode addr

inum1 iaddr1

inum2 iaddr2

inum3 iaddr3

Inode table

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Summary


Data blocks

inode

file1Inode number

Inode addr

inum1 iaddr1

inum2 iaddr2

inum3 iaddr3

Data blocks

inode

file2Inode table

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Summary


Data blocks

inode

file1Inode number

Inode addr

inum1 iaddr1

inum2 iaddr2

inum3 iaddr3

Data blocks

inode

file2Inode table

Filename Inode number

file1 inum1

file2 inum3

Directory

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Summary


Data blocks

inode

file1Inode number

Inode addr

inum1 iaddr1

inum2 iaddr2

inum3 iaddr3

Data blocks

inode

file2Inode table


file1 inum1

file2 inum3

Directory

cp file1 file3

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Summary


Data blocks

inode

file1Inode number

Inode addr

inum1 iaddr1

inum2 iaddr2

inum3 iaddr3

inum4 iaddr4

Data blocks

inode

file3Inode table


file1 inum1

file2 inum3

file3 inum4

Directory

cp file1 file3

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Summary


Data blocks

inode

file1Inode number

Inode addr

inum1 iaddr1

inum2 iaddr2

inum3 iaddr3

Data blocks

inode

file2Inode table


file1 inum1

file2 inum3

Directory

ln file1 file3

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Summary


Data blocks

inode

file1Inode number

Inode addr

inum1 iaddr1

inum2 iaddr2

inum3 iaddr3

Data blocks

inode

file2Inode table


file1 inum1

file2 inum3

file3 inum1

Directory

ln file1 file3

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Summary


Data blocks

inode

file1Inode number

Inode addr

inum1 iaddr1

inum2 iaddr2

inum3 iaddr3

Data blocks

inode

file2Inode table


file1 inum1

file2 inum3

Directory

ln –s file1 file3

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Summary


Data blocks

inode

file1Inode number

Inode addr

inum1 iaddr1

inum2 iaddr2

inum3 iaddr3

inum4 iaddr4

Data blocks“file1”

inode

file3Inode table


file1 inum1

file2 inum3

file3 inum4

Directory

ln –s file1 file3

inode inum4, iaddr4

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Access Permissions

• Operations on book/book1– ls book

• book ( r )

– cd book• book ( x )

– echo “this is a book” > book/book2• book ( wx )

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Access Permissions

• Operations on book/book1– ls book/book1

• book ( x )

– cat book/book1• book1 ( r ), book ( x )

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Access Permissions

• Operations on book/book1– rm book/book1

• book ( xw ), book1 ( w )

– cp book/book1 book/book2• book ( xw ), book1 ( r )

– mv book/book1 book/book3• book ( xw )

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Links

• Chained soft links– ln -s hello hello1– ln –s hello1 hello2

– rm hello1– cat hello2

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Links

• Permissions on links– ln hello hello1– ls –l hello hello1 hello2

– chmod a-r hello1– chmod a+r hello2

File Systems (ch 4) IT244 - Introduction to Linux / Unix Instructor: Bo Sheng 1.

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Transcript of File Systems (ch 4) IT244 - Introduction to Linux / Unix Instructor: Bo Sheng 1.