.\" Copyright (c) 2017-2018 Apple Computer, Inc. All rights reserved. .\" .\" The contents of this file constitute Original Code as defined in and .\" are subject to the Apple Public Source License Version 1.1 (the .\" "License"). You may not use this file except in compliance with the .\" License. Please obtain a copy of the License at .\" http://www.apple.com/publicsource and read it before using this file. .\" .\" This Original Code and all software distributed under the License are .\" distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER .\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, .\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, .\" FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the .\" License for the specific language governing rights and limitations .\" under the License. .\" .\" @(#)fs_snapshot_create.2 . .Dd July 4th, 2017 .Dt FS_SNAPSHOT_CREATE 2 .Os Darwin .Sh NAME .Nm fs_snapshot_create .Nd create read only snapshot of a mounted filesystem .Sh SYNOPSIS .Fd #include .Fd #include .Pp .Ft int .Fn fs_snapshot_create "int dirfd" "const char * name" "uint32_t flags" . .Ft int .Fn fs_snapshot_delete "int dirfd" "const char * name" "uint32_t flags" . .Ft int .Fn fs_snapshot_list "int dirfd" "struct attrlist * name" "void * attrbuf" "size_t bufsize" "uint32_t flags" . .Ft int .Fn fs_snapshot_rename "int dirfd" "const char * old" "const char * new" "uint32_t flags" . .Ft int .Fn fs_snapshot_mount "int dirfd" "const char * dir" "const char * snapshot" "uint32_t flags" . .Ft int .Fn fs_snapshot_revert "int dirfd" "const char * name" "uint32_t flags" . .Sh DESCRIPTION The .Fn fs_snapshot_create function, for supported Filesystems, causes a snapshot of the Filesystem to be created. A snapshot is a read only copy of the filesystem frozen at a point in time. The Filesystem is identified by the .Fa dirfd parameter which should be a file descriptor associated with the root directory of the filesystem for which the snapshot is to be created. .Fa name can be any valid name for a component name (except . and ..). . The .Fn fs_snapshot_delete function causes the named snapshot .Fa name to be deleted and the .Fn fs_snapshot_rename function causes the named snapshot .Fa old to be renamed to the name .Fa new . Available snapshots along with their attributes can be listed by calling .Fn fs_snapshot_list which is to be used in exactly the same way as .Xr getattrlistbulk 2 . . The .Fa flags parameter specifies the options that can be passed. No options are currently defined. .Pp Snapshots may be useful for backing up the Filesystem and to restore the Filesystem to a previous state. Snapshots are expected to consume no additional storage on creation but might consume additional storage as the active Filesystem is modified. Similarly deletion of files on the active filesystem may not result in the storage being available if the snapshot contains the file. Additionally, the underlying Filesystem may impose a limit on the number of snapshots that can be taken. For supporting Filesystems, a snapshot may be used as a source for a mount. This can be done by the .Fn fs_snapshot_mount function. The snapshot will be mounted read only. When a snapshot is mounted, it cannot be deleted but it can be renamed. To revert the filesystem to a previous snapshot, the .Fn fs_snapshot_revert can be used. It should be noted that reverting a filesystem to a snapshot is a destructive operation and causes all changes made to the filesystem (including snapshots created after the snapshot being reverted to) to be lost. . .Pp All snapshot functions require superuser privileges and also require an additional entitlement. . .Sh RETURN VALUES Upon successful completion, .Fn fs_snapshot_create , .Fn fs_snapshot_delete and .Fn fs_snapshot_rename returns 0. Otherwise, a value of -1 is returned and errno is set to indicate the error. .Fn fs_snapshot_list returns the number of entries successfully read. A return value of 0 indicates there are no more entries. Otherwise, a value of -1 is returned and errno is set to indicate the error. Return values are the same as .Xr getattrlistbulk 2 . .Pp .Sh COMPATIBILITY Not all volumes support snapshots. A volume can be tested for snapshot support by using .Xr getattrlist 2 to get the volume capabilities attribute ATTR_VOL_CAPABILITIES, and then testing the VOL_CAP_INT_SNAPSHOT flag. .Pp .Sh ERRORS The .Fn fs_snapshot_create , .Fn fs_snapshot_delete , .Fn fs_snapshot_rename and .Fn fs_snapshot_list function will fail if: .Bl -tag -width Er . .It Bq Er EACCES Read permissions are denied for the caller on the filesystem . .It Bq Er ENOTSUP The underlying filesystem does not support this call. . .It Bq Er EINVAL The value of the .Fa flags parameter is invalid. . .It Bq Er ENOSPC There is no free space remaining on the file system containing the file. . .It Bq Er ENOSPC The limit for the maximum number of snapshots for a filesystem has been reached. . .It Bq Er EIO An I/O error occurred while reading from or writing to the file system. . .It Bq Er EPERM The calling process does not have appropriate privileges. . .It Bq Er EROFS The requested operation requires modifications in a read-only file system. . .It Bq Er ENAMETOOLONG The length of a component of a pathname is longer than {NAME_MAX}. . .It Bq Er EBADF dirfd is not a valid file descriptor. . .It Bq Er ENOTDIR dirfd is a file descriptor associated with a non-directory file. .El .Pp In addition, the .Fn fs_snapshot_create or .Fn fs_snapshot_rename functions may fail with the following errors .Bl -tag -width Er .It Bq Er EEXIST The The named snapshot to be created already exists or the new name already exists for the snapshot being renamed. . .El .Pp .Fn fs_snapshot_create or .Fn fs_snapshot_rename functions may fail with the following errors .Bl -tag -width Er .It Bq Er ENOENT The named snapshot does not exist. .El . .Pp .Fn fs_snapshot_delete function may fail with .Bl -tag -width Er .It Bq Er EBUSY The named snapshot is currently mounted. .El . .Sh SEE ALSO . .Xr getattrlist 2 , .Xr getattrlistbulk 2 . .Sh HISTORY The .Fn fs_snapshot_create , .Fn fs_snapshot_delete , .Fn fs_snapshot_list , .Fn fs_snapshot_mount , .Fn fs_snapshot_rename and .Fn fs_snapshot_revert function calls appeared in macOS version 10.13 .