Linux File Systems

1. Linux File Systems Presented by: Lloyd Brown, James Frazee, & Travis Wertz

2. File System Capabilities • File types • Permissions

3. File Types • Regular Files • Directories • Links • Symbolic • Hard

4. Permissions • Old Unix-style Standard Permissions: • Universal • User, Group, Others • Example: user@host~$ ls -lh procmail.log -rw------- 1 lbrown lbrown 47K Mar 30 14:17 procmail.log

5. Permissions • Access Control List (ACL) • Allows arbitrary users/groups to be given permissions to files • Example: user@host# getfacl www # file: www # owner: root # group: clusterstat user::rwx user:36:r-x group::rwx group:clusterstat:rwx group:clusterstat_ro:r-x mask::rwx other::--- default:user::rwx default:user:36:r-x default:group::rwx default:group:clusterstat:rwx default:group:clusterstat_ro:r-x default:mask::rwx default:other::---

6. Virtual File Systems • Inodes • Dentrys • Superblocks

7. Inode • I(ndex)Node • Describes location of each file, directory, or link within every FS • Identified by a tuple containing unique number

8. Dentry • Directory Entry • Used to map file descriptors to inodes • Contains name of file or directory • File descriptor points to a dentry, which points to inode.

9. Dentry Example Dentry /home Pointer /home/chris /home/jim /home/chris/foo /home/chris/bar /home/chris/txt

10. Superblock • When FS is mounted, contents are attached to primary directory tree • Superblock contains information about mounted FS • Type • Root inode location • Items that protect integrity • Created by kernel • Resides in memory

11. Specific Types • General File Systems • Network File Systems • Special Purpose File Systems

12. General File Systems • Ext 2/3 • ReiserFS • JFS • XFS

13. Network File Systems • NFS • SMB/CIFS

14. Memory File Systems • ProcFS • TmpFS • SysFS • RamFS