The document discusses Linux file systems and files. Some key points include: - In Linux, everything is treated as a file with different attributes like regular files, directories, links, and devices. - Files have owners, groups, and permissions that control access for owners, groups, and others. - There is a predefined directory structure with important directories like /etc, /usr, /sbin, and users' home directories under /home. - Inodes store metadata about files like attributes, ownership, and locations of data blocks on the disk.

1. Linux File Systems and File
Minsuk Lee
Hansung University, Seoul, Korea
minsuk@hansung.ac.kr
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2. Linux File System
• In Linux, everything is a file.
– Its attribute is different
• Regular File, Directory, Link, Device
• Every file has owner and group.
• Every file has permission for
– owner, group, and others
• Prebuilt directory architecture :
– /etc, /dev, /usr, /sbin, /…
DON’T CHANGE IT !
YOU MANAGE YOUR OWN HOME DIRECTORY ~/
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3. Attribute of a File
• $ ls -l
Attr perm #link owner group file size date time filename
---------------------------------------------------------------------------------------
-rw-r--r-- 1 myuser myuser 164 2011-08-28 14:25 myfile
- rwx r-x r— File name :
0 7 5 4 256 characters
Case sensitive
Attribute user group other No extension
Most special characters accepted
Attribute:
- : regular file
b : block device permission:
c : character device r : readable
d : directory w : writable
l : symbolic link x : executable (traversable)
p : pipe
s : socket $ chmod, $chown work here !
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4. Inode (metadata for a File)
• Inode has information of a file
– Inode also exists in disk
– All the attributes, times, owner
– Data block locations
inode
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5. File link
• Link (hard link), Symbolic Link
디렉토리 Inode 블럭 Data 블럭
– myfile and myfile-link shares same disk space
• One good usage of hard link is to protect not to be erased accidentally
– myfile-sym-link is a link file with the target file name in it
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6. Permission Masking
• Default permission setting
– ‘$ umask mask ‘ : masking 666 (rw-rw-rw-) with mask
– default mask value = 022 (rw-r--r--)
– ‘x’ field cannot be masked
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7. Set UID option !
• Some commands needs to change other’s file
 Need some mechanism to run command with file owners permission
• $ chmod u+s <executable-file>
– Sets UID field in inode attributes
– Makes rwx to rws
THINK
SECURITY !!
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8. The Root Directory ‘/’ (1)
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9. The Root directory (2)
• / : the root directory (top most directory in the system)
– All absolute directory path starts with ‘/’
– There is NO ‘C:’, ‘D:’,
– every storage is mounted somewhere in directory hierarchy
• /cdrom, /mnt/floppy, …
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10. /dev (1)
• Device special files : the abstraction to access hardware devices
– block devices : hdd, cdrom, floppy disk, tape, USB memory
– character devices : serial port, …
– other devices
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11. /dev (2)
• IDE hdd
– brw-rw---- : b block device, user/group : rw
– Owner : root, group : disk
– Device Major, minor number : 8,0
– /dev/sda : the Whole IDE disk
• /dev/sda1, /dev/sda2, /dev/sda5 : partitions
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12. Partition table
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13. Other directories (1)
• /bin : Most frequently used commands
• /etc : Configuration File directory
– System itself, servers, applications, …
• /home : user’s home directories
• /lib : shared libraries, kernel modules
• /lost+found : area for file system check utility
• /mnt : default mount point (not mandatory)
– For removable storages (cdrom, usb, floppy, ...)
• /root : home directory for superuser
• /sbin : commands for system management
– fsck, ifconfig, lsmod, mkfs, reboot…
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14. Other directories (2)
• /tmp : directory for temporary data
• /var : directory for frequently changed data
– Logs, mail spool, print spool, lock files
• /sys. /proc : system monitoring (virtual)
• /usr : commands/library/data for users
• /boot : files for Boot
– Booting Process
• PowerON  ROM-BIOS (read MBR)  BootLoader  Kernel
• For embedded devices there is no ROM-BIOS
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15. Locating files
• $ which <filename>
– Search execution file in PATH
• $ whereis <filename>
– Search Execution file, source, man page file
• $ locate <filename-pattern>
– Search system for the pattern
• Works like ‘$ find ./ -name *pattern*’
– Needs ‘$ updatedb’ to refresh database
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16. Let’s practice !
• Make link and symbolic link for a file
– See what happen if erase files
• Erasing the link file, erasing the original file
• Apply umask and generate file with $vi
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