commit 3e500a8f116b0515d1507fe0ab4bf617664a6cdc Author: Eric Sandeen Date: Fri Jul 4 23:07:36 2014 -0400 e2fsprogs: add mount options to ext4.5 This is a straight cut and paste from the util-linux mount manpage to ext4.5 (with commented-out lines removed). It's pretty much impossible for util-linux to keep up with every filesystem out there, and Karel has more than once expressed a wish that mount options move into fs-specific manpages. So, here we go. Signed-off-by: Eric Sandeen Signed-off-by: Theodore Ts'o diff --git a/misc/ext4.5.in b/misc/ext4.5.in index 134c19f..9112b3d 100644 --- a/misc/ext4.5.in +++ b/misc/ext4.5.in @@ -251,10 +251,368 @@ and it also speeds up the time required for .BR mke2fs (8) to create the file system. .RE +.SH MOUNT OPTIONS +This section describes mount options which are specific to ext2, ext3, +and ext4. Other generic mount options may be used as well; see +.BR mount (8) +for details. +.SH "Mount options for ext2" +The `ext2' filesystem is the standard Linux filesystem. +Since Linux 2.5.46, for most mount options the default +is determined by the filesystem superblock. Set them with +.BR tune2fs (8). +.TP +.BR acl | noacl +Support POSIX Access Control Lists (or not). +.TP +.BR bsddf | minixdf +Set the behavior for the +.I statfs +system call. The +.B minixdf +behavior is to return in the +.I f_blocks +field the total number of blocks of the filesystem, while the +.B bsddf +behavior (which is the default) is to subtract the overhead blocks +used by the ext2 filesystem and not available for file storage. Thus +.sp 1 +% mount /k \-o minixdf; df /k; umount /k +.TS +tab(#); +l2 l2 r2 l2 l2 l +l c r c c l. +Filesystem#1024-blocks#Used#Available#Capacity#Mounted on +/dev/sda6#2630655#86954#2412169#3%#/k +.TE +.sp 1 +% mount /k \-o bsddf; df /k; umount /k +.TS +tab(#); +l2 l2 r2 l2 l2 l +l c r c c l. +Filesystem#1024-blocks#Used#Available#Capacity#Mounted on +/dev/sda6#2543714#13#2412169#0%#/k +.TE +.sp 1 +(Note that this example shows that one can add command line options +to the options given in +.IR /etc/fstab .) +.TP +.BR check=none " or " nocheck +No checking is done at mount time. This is the default. This is fast. +It is wise to invoke +.BR e2fsck (8) +every now and then, e.g.\& at boot time. The non-default behavior is unsupported +(check=normal and check=strict options have been removed). Note that these mount options +don't have to be supported if ext4 kernel driver is used for ext2 and ext3 filesystems. +.TP +.B debug +Print debugging info upon each (re)mount. +.TP +.BR errors= { continue | remount-ro | panic } +Define the behavior when an error is encountered. +(Either ignore errors and just mark the filesystem erroneous and continue, +or remount the filesystem read-only, or panic and halt the system.) +The default is set in the filesystem superblock, and can be +changed using +.BR tune2fs (8). +.TP +.BR grpid | bsdgroups " and " nogrpid | sysvgroups +These options define what group id a newly created file gets. +When +.B grpid +is set, it takes the group id of the directory in which it is created; +otherwise (the default) it takes the fsgid of the current process, unless +the directory has the setgid bit set, in which case it takes the gid +from the parent directory, and also gets the setgid bit set +if it is a directory itself. +.TP +.BR grpquota | noquota | quota | usrquota +The usrquota (same as quota) mount option enables user quota support on the +filesystem. grpquota enables group quotas support. You need the quota utilities +to actually enable and manage the quota system. +.TP +.B nouid32 +Disables 32-bit UIDs and GIDs. This is for interoperability with older +kernels which only store and expect 16-bit values. +.TP +.BR oldalloc " or " orlov +Use old allocator or Orlov allocator for new inodes. Orlov is default. +.TP +\fBresgid=\fP\,\fIn\fP and \fBresuid=\fP\,\fIn\fP +The ext2 filesystem reserves a certain percentage of the available +space (by default 5%, see +.BR mke2fs (8) +and +.BR tune2fs (8)). +These options determine who can use the reserved blocks. +(Roughly: whoever has the specified uid, or belongs to the specified group.) +.TP +.BI sb= n +Instead of block 1, use block +.I n +as superblock. This could be useful when the filesystem has been damaged. +(Earlier, copies of the superblock would be made every 8192 blocks: in +block 1, 8193, 16385, \&...\& (and one got thousands of copies on +a big filesystem). Since version 1.08, +.B mke2fs +has a \-s (sparse superblock) option to reduce the number of backup +superblocks, and since version 1.15 this is the default. Note +that this may mean that ext2 filesystems created by a recent +.B mke2fs +cannot be mounted r/w under Linux 2.0.*.) +The block number here uses 1\ k units. Thus, if you want to use logical +block 32768 on a filesystem with 4\ k blocks, use "sb=131072". +.TP +.BR user_xattr | nouser_xattr +Support "user." extended attributes (or not). + + +.SH "Mount options for ext3" +The ext3 filesystem is a version of the ext2 filesystem which has been +enhanced with journaling. It supports the same options as ext2 as +well as the following additions: +.TP +.B journal=update +Update the ext3 filesystem's journal to the current format. +.TP +.B journal=inum +When a journal already exists, this option is ignored. Otherwise, it +specifies the number of the inode which will represent the ext3 filesystem's +journal file; ext3 will create a new journal, overwriting the old contents +of the file whose inode number is +.IR inum . +.TP +.BR journal_dev=devnum / journal_path=path +When the external journal device's major/minor numbers +have changed, these options allow the user to specify +the new journal location. The journal device is +identified either through its new major/minor numbers encoded +in devnum, or via a path to the device. +.TP +.BR norecovery / noload +Don't load the journal on mounting. Note that +if the filesystem was not unmounted cleanly, +skipping the journal replay will lead to the +filesystem containing inconsistencies that can +lead to any number of problems. +.TP +.BR data= { journal | ordered | writeback } +Specifies the journaling mode for file data. Metadata is always journaled. +To use modes other than +.B ordered +on the root filesystem, pass the mode to the kernel as boot parameter, e.g.\& +.IR rootflags=data=journal . +.RS +.TP +.B journal +All data is committed into the journal prior to being written into the +main filesystem. +.TP +.B ordered +This is the default mode. All data is forced directly out to the main file +system prior to its metadata being committed to the journal. +.TP +.B writeback +Data ordering is not preserved \(en data may be written into the main +filesystem after its metadata has been committed to the journal. +This is rumoured to be the highest-throughput option. It guarantees +internal filesystem integrity, however it can allow old data to appear +in files after a crash and journal recovery. +.RE +.TP +.B data_err=ignore +Just print an error message if an error occurs in a file data buffer in +ordered mode. +.TP +.B data_err=abort +Abort the journal if an error occurs in a file data buffer in ordered mode. +.TP +.BR barrier=0 " / " barrier=1 " +This disables / enables the use of write barriers in the jbd code. barrier=0 +disables, barrier=1 enables (default). This also requires an IO stack which can +support barriers, and if jbd gets an error on a barrier write, it will disable +barriers again with a warning. Write barriers enforce proper on-disk ordering +of journal commits, making volatile disk write caches safe to use, at some +performance penalty. If your disks are battery-backed in one way or another, +disabling barriers may safely improve performance. +.TP +.BI commit= nrsec +Sync all data and metadata every +.I nrsec +seconds. The default value is 5 seconds. Zero means default. +.TP +.B user_xattr +Enable Extended User Attributes. See the +.BR attr (5) +manual page. +.TP +.B acl +Enable POSIX Access Control Lists. See the +.BR acl (5) +manual page. +.TP +.BR usrjquota=aquota.user | grpjquota=aquota.group | jqfmt=vfsv0 +Apart from the old quota system (as in ext2, jqfmt=vfsold aka version 1 quota) +ext3 also supports journaled quotas (version 2 quota). jqfmt=vfsv0 +enables journaled quotas. For journaled quotas the mount options +usrjquota=aquota.user and grpjquota=aquota.group are required to tell the +quota system which quota database files to use. Journaled quotas have the +advantage that even after a crash no quota check is required. + +.SH "Mount options for ext4" +The ext4 filesystem is an advanced level of the ext3 filesystem which +incorporates scalability and reliability enhancements for supporting large +filesystem. + +The options +.B journal_dev, norecovery, noload, data, commit, orlov, oldalloc, [no]user_xattr +.B [no]acl, bsddf, minixdf, debug, errors, data_err, grpid, bsdgroups, nogrpid +.B sysvgroups, resgid, resuid, sb, quota, noquota, grpquota, usrquota +.B usrjquota, grpjquota and jqfmt +are backwardly compatible with ext3 or ext2. +.TP +.B journal_checksum +Enable checksumming of the journal transactions. This will allow the recovery +code in e2fsck and the kernel to detect corruption in the kernel. It is a +compatible change and will be ignored by older kernels. +.TP +.B journal_async_commit +Commit block can be written to disk without waiting for descriptor blocks. If +enabled older kernels cannot mount the device. +This will enable 'journal_checksum' internally. +.TP +.BR barrier=0 " / " barrier=1 " / " barrier " / " nobarrier +These mount options have the same effect as in ext3. The mount options +"barrier" and "nobarrier" are added for consistency with other ext4 mount +options. + +The ext4 filesystem enables write barriers by default. +.TP +.BI inode_readahead_blks= n +This tuning parameter controls the maximum number of inode table blocks that +ext4's inode table readahead algorithm will pre-read into the buffer cache. +The value must be a power of 2. The default value is 32 blocks. +.TP +.BI stripe= n +Number of filesystem blocks that mballoc will try to use for allocation size +and alignment. For RAID5/6 systems this should be the number of data disks * +RAID chunk size in filesystem blocks. +.TP +.B delalloc +Deferring block allocation until write-out time. +.TP +.B nodelalloc +Disable delayed allocation. Blocks are allocated when data is copied from user +to page cache. +.TP +.BI max_batch_time= usec +Maximum amount of time ext4 should wait for additional filesystem operations to +be batch together with a synchronous write operation. Since a synchronous +write operation is going to force a commit and then a wait for the I/O +complete, it doesn't cost much, and can be a huge throughput win, we wait for a +small amount of time to see if any other transactions can piggyback on the +synchronous write. The algorithm used is designed to automatically tune for +the speed of the disk, by measuring the amount of time (on average) that it +takes to finish committing a transaction. Call this time the "commit time". +If the time that the transaction has been running is less than the commit time, +ext4 will try sleeping for the commit time to see if other operations will join +the transaction. The commit time is capped by the max_batch_time, which +defaults to 15000\ \[mc]s (15\ ms). This optimization can be turned off entirely by +setting max_batch_time to 0. +.TP +.BI min_batch_time= usec +This parameter sets the commit time (as described above) to be at least +min_batch_time. It defaults to zero microseconds. Increasing this parameter +may improve the throughput of multi-threaded, synchronous workloads on very +fast disks, at the cost of increasing latency. +.TP +.BI journal_ioprio= prio +The I/O priority (from 0 to 7, where 0 is the highest priority) which should be +used for I/O operations submitted by kjournald2 during a commit operation. +This defaults to 3, which is a slightly higher priority than the default I/O +priority. +.TP +.B abort +Simulate the effects of calling ext4_abort() for +debugging purposes. This is normally used while +remounting a filesystem which is already mounted. +.TP +.BR auto_da_alloc | noauto_da_alloc +Many broken applications don't use fsync() when +replacing existing files via patterns such as + +fd = open("foo.new")/write(fd,...)/close(fd)/ rename("foo.new", "foo") + +or worse yet + +fd = open("foo", O_TRUNC)/write(fd,...)/close(fd). + +If auto_da_alloc is enabled, ext4 will detect the replace-via-rename and +replace-via-truncate patterns and force that any delayed allocation blocks are +allocated such that at the next journal commit, in the default data=ordered +mode, the data blocks of the new file are forced to disk before the rename() +operation is committed. This provides roughly the same level of guarantees as +ext3, and avoids the "zero-length" problem that can happen when a system +crashes before the delayed allocation blocks are forced to disk. +.TP +.B noinit_itable +Do not initialize any uninitialized inode table blocks in the background. This +feature may be used by installation CD's so that the install process can +complete as quickly as possible; the inode table initialization process would +then be deferred until the next time the filesystem is mounted. +.TP +.B init_itable=n +The lazy itable init code will wait n times the number of milliseconds it took +to zero out the previous block group's inode table. This minimizes the impact on +system performance while the filesystem's inode table is being initialized. +.TP +.BR discard / nodiscard +Controls whether ext4 should issue discard/TRIM commands to the underlying +block device when blocks are freed. This is useful for SSD devices and +sparse/thinly-provisioned LUNs, but it is off by default until sufficient +testing has been done. +.TP +.B nouid32 +Disables 32-bit UIDs and GIDs. This is for +interoperability with older kernels which only +store and expect 16-bit values. +.TP +.BR block_validity / noblock_validity +This options allows to enables/disables the in-kernel facility for tracking +filesystem metadata blocks within internal data structures. This allows multi-\c +block allocator and other routines to quickly locate extents which might +overlap with filesystem metadata blocks. This option is intended for debugging +purposes and since it negatively affects the performance, it is off by default. +.TP +.BR dioread_lock / dioread_nolock +Controls whether or not ext4 should use the DIO read locking. If the +dioread_nolock option is specified ext4 will allocate uninitialized extent +before buffer write and convert the extent to initialized after IO completes. +This approach allows ext4 code to avoid using inode mutex, which improves +scalability on high speed storages. However this does not work with data +journaling and dioread_nolock option will be ignored with kernel warning. +Note that dioread_nolock code path is only used for extent-based files. +Because of the restrictions this options comprises it is off by default +(e.g.\& dioread_lock). +.TP +.B max_dir_size_kb=n +This limits the size of the directories so that any attempt to expand them +beyond the specified limit in kilobytes will cause an ENOSPC error. This is +useful in memory-constrained environments, where a very large directory can +cause severe performance problems or even provoke the Out Of Memory killer. (For +example, if there is only 512\ MB memory available, a 176\ MB directory may +seriously cramp the system's style.) +.TP +.B i_version +Enable 64-bit inode version support. This option is off by default. + .SH SEE ALSO .BR mke2fs (8), .BR mke2fs.conf (5), .BR e2fsck (8), .BR dumpe2fs (8), .BR tune2fs (8), -.BR debugfs (8) +.BR debugfs (8), +.BR mount (8)