Documentation/filesystems/ext2.rst

1 .. SPDX-License-Identifier: GPL-2.0
18 set using tune2fs(8). Kernel-determined defaults are indicated by (*).
34 errors=remount-ro		Remount the filesystem read-only on an error.
40 nouid32				Use 16-bit UIDs and GIDs.
84 ------
93 ------------
101 are in use.  Since each bitmap is limited to a single block, this means
110 --------------
140 ------
155 larger than 2GB).  The translator field is unused under Linux, but is used
164 pointers to the next set of blocks), a pointer to a doubly-indirect
166 trebly-indirect block (which contains pointers to doubly-indirect blocks).
168 The flags field contains some ext2-specific flags which aren't catered
171 behaviour on a per-file basis.  There are flags for secure deletion,
172 undeletable, compression, synchronous updates, immutability, append-only,
173 dumpable, no-atime, indexed directories, and data-journaling.  Not all
177 -----------
190 The current implementation of ext2 uses a singly-linked list to store
198 -------------
212 --------------
215 for a particular user (normally the super-user).  This is intended to
216 allow for the system to continue functioning even if non-privileged users
222 ----------------
233 ---------------------
240 revision 1.  There are three 32-bit fields, one for compatible features
241 (COMPAT), one for read-only compatible (RO_COMPAT) features and one for
247 but the on-disk format is 100% compatible with older on-disk formats, so
257 An RO_COMPAT flag indicates that the on-disk format is 100% compatible
258 with older on-disk formats for reading (i.e. the feature does not change
259 the visible on-disk format).  However, an old kernel writing to such a
268 An INCOMPAT flag indicates the on-disk format has changed in some
273 The COMPRESSION flag is an obvious INCOMPAT flag - if the kernel
290 --------
300 - per-file if you have the program source: use the O_SYNC flag to open()
301 - per-file if you don't have the source: use "chattr +S" on the file
302 - per-filesystem: add the "sync" option to mount (or in /etc/fstab)
308 -----------
310 There are various limits imposed by the on-disk layout of ext2.  Other
318 Most of these limits could be overcome with slight changes in the on-disk
329 There is a 2.4 kernel limit of 2048GB for a single block device, so no
335 There is an upper limit of 32000 subdirectories in a single directory.
337 There is a "soft" upper limit of about 10-15k files in a single directory
338 with the current linear linked-list directory implementation.  This limit
341 (under development) allows 100k-1M+ files in a single directory without
344 The (meaningless) absolute upper limit of files in a single directory
347 enough 4-character names to make up unique directory entries, so they
352 ----------
357 to the on-disk ext2 layout.  In a nutshell, the journal is a regular
364 a transaction in the journal and can either be complete or incomplete at
365 the time of a crash.  If a transaction is complete at the time of a crash
367 in that transaction are guaranteed to represent a valid filesystem state,
368 and are copied into the filesystem.  If a transaction is incomplete at
370 the blocks in that transaction so they are discarded (which means any
394 RISC OS client		http://www.esw-heim.tu-clausthal.de/~marco/smorbrod/IscaFS/