Free Knowledge Resources


Linux Manual Pages


Free Software * Books

Source Code

Free Media

Linux

btrfs-rescue(8)


NAME

   btrfs-rescue - Recover a damaged btrfs filesystem

SYNOPSIS

   btrfs rescue <subcommand> <args>

DESCRIPTION

   btrfs rescue is used to try to recover a damaged btrfs filesystem.

SUBCOMMAND

   chunk-recover [options] <device>
       Recover the chunk tree by scanning the devices

       Options

       -y
           assume an answer of yes to all questions.

       -v
           verbose mode.

       -h
           help.

       Note
       Since chunk-recover will scan the whole device, it will be VERY
       slow especially executed on a large device.

   super-recover [options] <device>
       Recover bad superblocks from good copies.

       Options

       -y
           assume an answer of yes to all questions.

       -v
           verbose mode.

   zero-log <device>
       clear the filesystem log tree

   This command will clear the filesystem log tree. This may fix a
   specific set of problem when the filesystem mount fails due to the log
   replay. See below for sample stacktraces that may show up in system
   log.

   The common case where this happens has been fixed a long time ago, so
   it is unlikely that you will see this particular problem, but the
   utility is kept around.

       Note
       clearing the log may lead to loss of changes that were made since
       the last transaction commit. This may be up to 30 seconds (default
       commit period) or less if the commit was implied by other
       filesystem activity.

   One can determine whether zero-log is needed according to the kernel
   backtrace:

       ? replay_one_dir_item+0xb5/0xb5 [btrfs]
       ? walk_log_tree+0x9c/0x19d [btrfs]
       ? btrfs_read_fs_root_no_radix+0x169/0x1a1 [btrfs]
       ? btrfs_recover_log_trees+0x195/0x29c [btrfs]
       ? replay_one_dir_item+0xb5/0xb5 [btrfs]
       ? btree_read_extent_buffer_pages+0x76/0xbc [btrfs]
       ? open_ctree+0xff6/0x132c [btrfs]

   If the errors are like above, then zero-log should be used to clear the
   log and the filesystem may be mounted normally again. The keywords to
   look for are open_ctree which says that it's during mount and function
   names that contain replay, recover or log_tree.

EXIT STATUS

   btrfs rescue returns a zero exit status if it succeeds. Non zero is
   returned in case of failure.

AVAILABILITY

   btrfs is part of btrfs-progs. Please refer to the btrfs wiki
   http://btrfs.wiki.kernel.org for further details.

SEE ALSO

   mkfs.btrfs(8), btrfs-scrub(8), btrfs-check(8)



Opportunity


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.



Free Software


Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.



Free Books


The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.



Education


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.


birds banner