What this means is that any changes to a file are immediately written to disk and available. D – Sychronous Directory Updates: When a change is made to the file changes are written synchronously to the disk.d -no dump: This marks the file as not being a candidate for backups when the dump command is used.This behavior can be turned off by setting the C attribute so that a separate, private copy is never created. Should a task write to the file, then a private copy is broken off for that task instead of manipulating the shared resource. C – no copy-on-write: The standard behavior on most Linux file systems is that when a file is opened by multiple tasks at one time, instead of creating multiple copies of the information for each task, a pointer to the shared resource is used.Note that this attribute is not honored by ext2 and ext3 file systems. Note that setting this attribute can incur overhead as the file will need to be compressed and uncompressed when written to or accessed. Data written to the file is compressed by the kernel before the file is written and when read, the file is uncompressed by the kernel for the read. c – compressed attribute: Compress sets the file to be compressed when written to on the disk.You would actually have to modify the file and then access it (e.g cat the file) before the atime would change. So if you are monitoring the atime with stat on a file and you are accessing the file and not seeing this time stamp change, chances are the file system you are on is mounted with noatime or relatime set. Now it could be set in strict mode where atime is always updated when the file is accesses or with relatime which only update the access time should it be older than the modification time when the file is accessed. With atime set use the kernel defaults for how atime is set. With noatime set the access time of the file is not updated when the file is accessed. The behavior of atime is determine by how the file system is mounted. This attribute can be a little tricky because if you want to see it in action you need to be aware of a few things. When the file is accessed do not update the access time (atime) attribute. A – Do not update Atime – access time.This attribute can only be set by an account with superuser privileges. Most normal file edit operations, like opening the file with a text editor, will most likely fail as the program will attempt to overwrite the file with the changes and “permission denied” will be displayed. That is you cannot redirect output to overwrite the file, only append to it. a – append only: Writing to a file will only allow the file to be opened in append mode for writing.The extended attributes provide the following manipulable behaviors ordered by their labels: Extended attributes are currently supported in the ext file systems along with JFS, ReiserFS, XFS, Btrfs, and OCFS2 version 1.6. Extended attributes, abbreviated xattr, add some more permissions or restrictions to the original three attributes. Recall that Linux file systems support three permission attributes: Read, write and execute for three different levels: Owner, owning group, and everyone else. This episode is going to extend that and talk about file system attributes, or more appropriately named extended attributes. Back in episode 7 the chown command and UNIX file permissions were discussed.
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