Ссылки по теме * [File permissions and attributes](/index.php/File_permissions_and_attributes "File permissions and attributes") **Состояние перевода:** На этой странице представлен перевод статьи [Umask](/index.php/Umask "Umask"). Дата последней синхронизации: 24 июля 2017\. Вы можете [помочь](/index.php/ArchWiki_Translation_Team_(%D0%A0%D1%83%D1%81%D1%81%D0%BA%D0%B8%D0%B9) "ArchWiki Translation Team (Русский)") синхронизировать перевод, если в английской версии произошли [изменения](https://wiki.archlinux.org/index.php?title=Umask&diff=0&oldid=482814). The *umask* utility is used to control the file-creation mode mask, which determines the initial value of file permission bits for newly created files. The behaviour of this utility is standardized by [POSIX](https://en.wikipedia.org/wiki/POSIX "wikipedia:POSIX") and described in the [POSIX Programmer's Manual](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/umask.html). Because *umask* affects the current shell execution environment, it is usually implemented as built-in command of a shell. ## Contents * [1 Meaning of the mode mask](#Meaning_of_the_mode_mask) * [2 Display the current mask value](#Display_the_current_mask_value) * [3 Set the mask value](#Set_the_mask_value) * [4 See also](#See_also) ## Meaning of the mode mask The mode mask contains the permission bits that should **not** be set on a newly created file, hence it is the [logical complement](https://en.wikipedia.org/wiki/Logical_complement "wikipedia:Logical complement") of the permission bits set on a newly created file. If some bit in the mask is set to `1`, the corresponding permission for the newly created file will be disabled. Hence the mask acts as a filter to strip away permission bits and helps with setting default access to files. The resulting value for permission bits to be set on a newly created file is calculated using bitwise [material nonimplication](https://en.wikipedia.org/wiki/Material_nonimplication "wikipedia:Material nonimplication") (also known as abjunction), which can be expressed in logical notation: ``` R: (D & (~M)) ``` That is, the resulting permissions `R` are the result of [bitwise conjunction](https://en.wikipedia.org/wiki/Logical_conjunction "wikipedia:Logical conjunction") of default permissions `D` and the [bitwise negation](https://en.wikipedia.org/wiki/Bitwise_negation "wikipedia:Bitwise negation") of file-creation mode mask `M`. **Note:** * Linux does not allow a file to be created with execution permissions, in fact the default creation permissions are 777 for directories, but only 666 for files. * On Linux, only the file permission bits of the mask are used - see [umask(2)](https://jlk.fjfi.cvut.cz/arch/manpages/man/umask.2). The *suid*, *sgid* and *sticky* bits of the mask are ignored. For example, let us assume that the file-creation mode mask is 027\. Here the bitwise representation of each digit represents: * 0 stands for the *user* permission bits not set on a newly created file * 2 stands for the *group* permission bits not set on a newly created file * 7 stands for the *other* permission bits not set on a newly created file With the information provided by the table below this means that for a newly created file, for example owned by `User1` user and `Group1` group, `User1` has all the possible permissions (octal value 7) for the newly created file, other users of the `Group1` group do not have write permissions (octal value 5), and any other user does not have any permissions (octal value 0) to the newly created file. So with the 027 mask taken for this example, files will be created with 750 permissions. | Octal | Binary | Meaning | | 0 | 000 | no permissions | | 1 | 001 | execute only | | 2 | 010 | write only | | 3 | 011 | write and execute | | 4 | 100 | read only | | 5 | 101 | read and execute | | 6 | 110 | read and write | | 7 | 111 | read, write and execute | ## Display the current mask value To display the current mask, simply invoke *umask* without specifying any arguments. The default output style depends on implementation, but it is usually octal: `$ umask` `0027` When the `-S` option, standardized by POSIX, is used, the mask will be displayed using symbolic notation. However, the **symbolic notation value will always be the logical complement of the octal value**, i.e. the permission bits to be set on the newly created file: `$ umask -S` `u=rwx,g=rx,o=` ## Set the mask value **Note:** Umask values can be set on a case-by-case basis. For example, desktop users may find the restricted permissions on their home folder (`chmod 700`, as applied by `useradd -m`) sufficient, as they make all files within unaccessible to other users. Should this not be practical (for example when using [Apache](/index.php/Apache "Apache")), and public files are stored amongst private ones, then consider restricting the umask instead. You can set the umask value through the *umask* command. The string specifying the mode mask follows the same syntactic rules as the mode argument of [chmod](/index.php/Chmod "Chmod") (see the [POSIX Programmer's Manual](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/chmod.html#tag_20_17_13) for details). Most Linux distributions set a default value of `022`, including Arch[[1]](https://projects.archlinux.org/svntogit/packages.git/tree/trunk/profile?h=packages/filesystem) or `002` in `/etc/profile` or in the default [shell](/index.php/Shell "Shell") configuration files, e.g. `/etc/bashrc`. If you need to set a different value, you can either directly edit such file, thus affecting all users, or call *umask* from your shell's user configuration file, e.g. `~/.bashrc` to only change your umask, however these changes will only take effect after the next login. To change your umask during your current session only, simply run *umask* and type your desired value. For example, running `umask 077` will give you read and write permissions for new files, and read, write and execute permissions for new folders. ## See also * POSIX Programmer's Manual: * [umask](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/umask.html) (also available as `umask(1P)`) * [chmod (extended description)](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/chmod.html#tag_20_17_13) (also available as `chmod(1P)`) * [wikipedia:umask](https://en.wikipedia.org/wiki/umask "wikipedia:umask") * [027 umask: a compromise](https://blogs.gentoo.org/mgorny/2011/10/18/027-umask-a-compromise-between-security-and-simplicity/)