Ограничения длины имени файла на Linux?
Есть ли какие-либо ограничения на длину файла или пути в Linux?
См. Страницу Википедии о сравнении файловых систем , особенно в столбце Максимальная длина имени файла .
Вот некоторые ограничения длины имени файла в популярных файловых системах:
Я читал здесь, что ограничение длины пути в системных заголовках. Ограничение длины имени файла тоже там. В моей системе это файл:
и C-lang определяет:
Я имею в виду другие ответы, пожалуйста, проголосуйте за них.
Есть ли какие-либо ограничения на длину файла или пути в Linux?
Да, длина имени файла и пути ограничена:
Чтобы динамически получить эти свойства:
- Используйте функции pathconf и fpathconf как предложено Майклом Аароном Сафяном
- Создайте имя файла (или путь к файлу ) длиннее и длиннее, как объяснено dogbane
Используйте команду, getconf предложенную Тимом, которая также доступна в Linux:
И ради экономии времени (и привязки его к памяти):
ext2, ext3, ext4, zfs: без ограничений пути; Ограничение имени файла 255 байт.
Это длины имен файловых систем. У самого «linux» тоже есть. Например, из бит / stdio_lim.h:
Там нет никакого способа , чтобы определить максимальную длину путей на Linux переносимым способом. В моей системе:
Но я могу легко создавать пути намного длиннее, чем 4096 символов. Вместо этого смотрите PATH_MAX как нижнюю границу. Вы гарантированно сможете создавать пути так долго, но вы также можете создавать гораздо более длинные.
Вы всегда должны использовать pathconf или какую-либо функцию, подобную этой, чтобы получить значение времени выполнения для указанных элементов, поскольку на этой странице сказано, что:
Однако следует отметить, что многие из перечисленных пределов не являются инвариантными, и во время выполнения значение предела может отличаться от значений, указанных в этом заголовке, по следующим причинам:
Предел зависит от имени пути.
Предел различается между компиляцией и машинами времени выполнения.
По этим причинам приложение может использовать функции fpathconf (), pathconf () и sysconf () для определения фактического значения лимита во время выполнения.
Limit on file name length in bash
The following questions are meant for bash and linux only:
- Is there a limit on the number of characters in the absolute path name of a file?
- Is there a limit on the number of characters for the filename (without extension) only?
If so, what might these limits be? How can I access them in case they are system specific?
9 Answers 9
It depends very much on the filesystem. For the ext FS (currently the most used on Linux):
- max filename length: 255 bytes
- max path length: none
The extension is not something the FS is aware of, it 255 bytes, extension included (you can have file names without any extensions).
Here is a more exhaustive list of these limits, per FS.
There can also be extensions to your file system that can change your maximum length as well. For example, eCryptFS which uses part of the lower file name to keep metadata and limits the file name to a maximum length of 143 characters. See Ubuntu eCryptFS launchpad entry.
Filename length limits on linux?
Are there any filename or path length limits on Linux?
8 Answers 8
See the Wikipedia page about file systems comparison, especially in column Maximum filename length.
Here are some filename length limits in popular file systems:
I’ve read here that path length limit is in system headers. File name length limit is there too. On my system it’s file:
I refer to other answers, please upvote them.
Are there any filename or path length limits on Linux?
Yes, filename and pathname lengths are limited by :
- file-system limits as stated by WerkkreW ;
- constants defined in linux/limits.h as stated by sfp.
To dynamically get these properties:
- Use functions pathconf and fpathconf as proposed by Michael Aaron Safyan
- Create a filename (or pathname) longer and longer as explained by dogbane
Use the command getconf as proposed by tim that is also available on Linux:
And for the sake of saving time (and anchoring it to memory):
ext2, ext3, ext4, zfs: no pathname limits; 255 bytes filename limit.
Those are file system name lengths. «linux» itself has some too. For instance, from bits/stdio_lim.h:
There is no way to determine the maximum length of paths on Linux in a portable way. On my system:
But I can easily create paths much longer than 4096 characters. Instead see PATH_MAX as a lower bound. You are guaranteed to be able to create paths this long, but you might also be able to create much longer ones.
You should always use pathconf or some function like this to get the runtime value about the specified items, as this page said that:
It should be noted, however, that many of the listed limits are not invariant, and at runtime, the value of the limit may differ from those given in this header, for the following reasons:
The limit is pathname-dependent.
The limit differs between the compile and runtime machines.
For these reasons, an application may use the fpathconf(), pathconf(), and sysconf() functions to determine the actual value of a limit at runtime.
Programmatically determine maximum filename length
How can I determine the maximum filename length on a linux box?
Preferred in PHP programming language.
5 Answers 5
You want pathconf or fpathconf , which are not exposed (yet) in PHP. (When they are, they’ll probably be posix_pathconf .)
You may also shell out to getconf , a command-line utility interface to the same functionality. Try this on your system:
$ getconf NAME_MAX /tmp
$ getconf PATH_MAX /tmp
there’s no need to programatically determine it. it’s 255 bytes.
edit: you can have longer filenames on a very few file systems (reiser, i believe), but if you stick to 255 your app will be usable on any linux installation.
The maximum file length for most linux file systems is 255. You’re probably best off using that as a generic constant and modifying to fit your known file system in linux. Here’s a nice comparison of the file systems that might be used. Max file length is listed there.
You can use the constant PHP_MAXPATHLEN
I think you could use realpath(). I’m not sure best approach, but for example:
What is the maximum allowed filename (and folder) size with eCryptfs?
I am a new eCryptfs user and I have a very basic question that I wasn’t able to find anywhere. I am interested in using eCryptfs via my Synology NAS that uses Linux.
While trying to encrypt my folder (EXT4) via Synology’s encryption app (eCryptfs) I encounter errors that state that my filename length can not exceed 45 characters in length (so, no encryption).
If the limit really is 45 characters, eCryptfs may not be a usable tool for most.
What is the maximum allowed filename size when encrypting files and folders with eCryptfs? Is Linux 255 characters?
4 Answers 4
Full disclosure: I am one of the authors and the current maintainer of the eCryptfs userspace utilities.
Linux has a maximum filename length of 255 characters for most filesystems (including EXT4), and a maximum path of 4096 characters.
eCryptfs is a layered filesystem. It stacks on top of another filesystem such as EXT4, which is actually used to write data to the disk. eCryptfs always encrypts file contents, but it can optionally encrypt (obscure) filenames (or not).
If filenames are not encrypted, then you can safely write filenames of up to 255 characters and encrypt their contents, as the filenames written to the lower filesystem will simply match. While an attacker would not be able to read the contents of index.html or budget.xls , they would know what file names exist. That may (or may not) leak sensitive information depending on your use case.
If filenames are encrypted, things get a little more complicated. eCryptfs prepends a bit of data on the front of the encrypted filename, such that it can identify encrypted filenames definitively. Also, the encryption itself involves «padding» the filename.
For instance, I have an encrypted file,
/.bashrc . This filename is encrypted using my key to:
Clearly, that 7 character filename now requires more than 7 characters to be encrypted. Empirically, we have found that character filenames longer than 143 characters start requiring >255 characters to encrypt. So we (as eCryptfs upstream developers) typically recommend you limit your filenames to
Now, all that said, the Synology NAS is a commercial product that embeds and uses eCryptfs and Linux to encrypt and secure data on the device. We (the upstream developers of eCryptfs) have nothing to do with Synology or their products, though we’re generally happy to see eCryptfs used in the wild. It seems to me that their recommendation of 45 characters is either a typographical error (from our 140 character recommendation), or simply a far more conservative estimate.