4.6 create and change hard and symbolic links v2
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This document discusses hard and symbolic links in Linux file systems. It defines hard links as additional references to an inode that maintain the same permissions and access times as the original file. Symbolic links store the file path separately and can span file systems. The document provides instructions for creating hard and symbolic links using the ln command and explains how to identify them by listing directory contents. It also describes how multiple links can reference a single file and what happens when files or links are deleted.
4.6 create and change hard and symbolic links v2
- 2. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Key Knowledge Areas Create links. Identify hard and/or softlinks. Copying versus linking files. Use links to support system administration tasks. Devices, Linux Filesystems, Filesystem Hierarchy Standard Create and change hard and symbolic links Terms and Utilities ln 2
- 3. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Create and change hard and symbolic links Disk file format 3
- 4. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Create and change hard and symbolic links Disk Block Groups 4 • On the physical drive, information is stored in blocks • The first block is always the boot block • The rest of the blocks are pooled and organized into block groups • Each block groups contains a copy of super block and descriptions of all the block groups • Superblock holds information on the entire filesystem • Block and inode bitmaps provide fast lookup info on free and allocated blocks and inodes
- 5. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Create and change hard and symbolic links Disk Block Groups 5 • The inode table holds all of the inodes • The data blocks contain the actual data that is contained in the files on the filesystem
- 6. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Create and change hard and symbolic links inodes 6 Inodes, or Information Nodes, hold all of the meta information for a file Details about ownership, size, permissions, times, ACLs and more are stored in the inode. Most importantly, the inode points to data blocks which store the contents of the file.
- 7. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Create and change hard and symbolic links inodes 7 File Name of a file isn’t stored in a inode. That’s where directories come in... A directory is a special type of file whose contents (in the data blocks) is a list of name/inode pairs.
- 8. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Hard link hard link maintains the same permissions and access times of the original file both have same inode number - simply appears to have different filename and/or location 8 Create and change hard and symbolic links •Changes to either the original file or the link affect both. •The two files have equal importance. But deleting either of files won’t affect the other. •Hard link files appear to be regular files when examined and they function this way as well • Normal users can’t create hard links to directories. • Also, hard links aren’t allowed to span file systems To create a hard link, use the ln command # ln stuff2 /home/angie/stuff # ls –al -rw-r--r-- 2 root root 89704 Aug 27 2000 stuff -rw-r--r-- 2 root root 89704 Aug 27 2000 stuff2 Ex:
- 9. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Create and change hard and symbolic links Hard links 9 • When a new hard link is created, it simply adds another reference (filename) in a directory to that inode (file) • Removing a hard link does not remove file unless it was the only hard link to that inode • Hard links, due to their nature with inodes and directories, only operate within a filesystem - you can not create a hard link from one filesystem to another
- 10. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Symbolic link Users can create symbolic links to directories, and symbolic links can span file systems. 10 Create and change hard and symbolic links • Symbolic link maintains permissions separate from those of the original file. • Deleting the original file won’t remove the symbolic link, but the link wont funtion. To create a soft link, you use the ln command. # ln –s stuff /home/angie/stuffEx: Soft links can be identified by listing the details of a directory’s contents: # ls –al lrwxrwxrwx 1 angie angie 7 Mar 10 17:06 stuff -> /fun/stuff Ex:
- 11. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Create and change hard and symbolic links Symbolic links 11
- 12. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Create and change hard and symbolic links Symbolic Links to Different File Systems 12
- 13. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Create and change hard and symbolic links Multiple Links to One File 13