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Diffstat (limited to 'lib/libsys/chmod.2')
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diff --git a/lib/libsys/chmod.2 b/lib/libsys/chmod.2 new file mode 100644 index 000000000000..e496b773ddf8 --- /dev/null +++ b/lib/libsys/chmod.2 @@ -0,0 +1,357 @@ +.\" Copyright (c) 1980, 1991, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.Dd March 30, 2021 +.Dt CHMOD 2 +.Os +.Sh NAME +.Nm chmod , +.Nm fchmod , +.Nm lchmod , +.Nm fchmodat +.Nd change mode of file +.Sh LIBRARY +.Lb libc +.Sh SYNOPSIS +.In sys/stat.h +.Ft int +.Fn chmod "const char *path" "mode_t mode" +.Ft int +.Fn fchmod "int fd" "mode_t mode" +.Ft int +.Fn lchmod "const char *path" "mode_t mode" +.Ft int +.Fn fchmodat "int fd" "const char *path" "mode_t mode" "int flag" +.Sh DESCRIPTION +The file permission bits of the file named specified by +.Fa path +or referenced by the file descriptor +.Fa fd +are changed to +.Fa mode . +The +.Fn chmod +system call verifies that the process owner (user) either owns +the file specified by +.Fa path +(or +.Fa fd ) , +or +is the super-user. +The +.Fn chmod +system call follows symbolic links to operate on the target of the link +rather than the link itself. +.Pp +The +.Fn lchmod +system call is similar to +.Fn chmod +but does not follow symbolic links. +.Pp +The +.Fn fchmodat +is equivalent to either +.Fn chmod +or +.Fn lchmod +depending on the +.Fa flag +except in the case where +.Fa path +specifies a relative path. +In this case the file to be changed is determined relative to the directory +associated with the file descriptor +.Fa fd +instead of the current working directory. +The values for the +.Fa flag +are constructed by a bitwise-inclusive OR of flags from the following list, defined +in +.In fcntl.h : +.Bl -tag -width indent +.It Dv AT_SYMLINK_NOFOLLOW +If +.Fa path +names a symbolic link, then the mode of the symbolic link is changed. +.It Dv AT_RESOLVE_BENEATH +Only walk paths below the directory specified by the +.Ar fd +descriptor. +See the description of the +.Dv O_RESOLVE_BENEATH +flag in the +.Xr open 2 +manual page. +.It Dv AT_EMPTY_PATH +If the +.Fa path +argument is an empty string, operate on the file or directory +referenced by the descriptor +.Fa fd . +If +.Fa fd +is equal to +.Dv AT_FDCWD , +operate on the current working directory. +.El +.Pp +If +.Fn fchmodat +is passed the special value +.Dv AT_FDCWD +in the +.Fa fd +parameter, the current working directory is used. +If also +.Fa flag +is zero, the behavior is identical to a call to +.Fn chmod . +.Pp +A mode is created from +.Em or'd +permission bit masks +defined in +.In sys/stat.h : +.Pp +.Bd -literal -offset indent -compact +#define S_IRWXU 0000700 /* RWX mask for owner */ +#define S_IRUSR 0000400 /* R for owner */ +#define S_IWUSR 0000200 /* W for owner */ +#define S_IXUSR 0000100 /* X for owner */ + +#define S_IRWXG 0000070 /* RWX mask for group */ +#define S_IRGRP 0000040 /* R for group */ +#define S_IWGRP 0000020 /* W for group */ +#define S_IXGRP 0000010 /* X for group */ + +#define S_IRWXO 0000007 /* RWX mask for other */ +#define S_IROTH 0000004 /* R for other */ +#define S_IWOTH 0000002 /* W for other */ +#define S_IXOTH 0000001 /* X for other */ + +#define S_ISUID 0004000 /* set user id on execution */ +#define S_ISGID 0002000 /* set group id on execution */ +#define S_ISVTX 0001000 /* sticky bit */ +.Ed +.Pp +The non-standard +.Dv S_ISTXT +is a synonym for +.Dv S_ISVTX . +.Pp +The +.Fx +VM system totally ignores the sticky bit +.Pq Dv S_ISVTX +for executables. +On UFS-based file systems (FFS, LFS) the sticky +bit may only be set upon directories. +.Pp +If mode +.Dv S_ISVTX +(the `sticky bit') is set on a directory, +an unprivileged user may not delete or rename +files of other users in that directory. +The sticky bit may be +set by any user on a directory which the user owns or has appropriate +permissions. +For more details of the properties of the sticky bit, see +.Xr sticky 7 . +.Pp +If mode ISUID (set UID) is set on a directory, +and the MNT_SUIDDIR option was used in the mount of the file system, +then the owner of any new files and sub-directories +created within this directory are set +to be the same as the owner of that directory. +If this function is enabled, new directories will inherit +the bit from their parents. +Execute bits are removed from +the file, and it will not be given to root. +This behavior does not change the +requirements for the user to be allowed to write the file, but only the eventual +owner after it has been created. +Group inheritance is not affected. +.Pp +This feature is designed for use on fileservers serving PC users via +ftp, SAMBA, or netatalk. +It provides security holes for shell users and as +such should not be used on shell machines, especially on home directories. +This option requires the SUIDDIR +option in the kernel to work. +Only UFS file systems support this option. +For more details of the suiddir mount option, see +.Xr mount 8 . +.Pp +Writing or changing the owner of a file +turns off the set-user-id and set-group-id bits +unless the user is the super-user. +This makes the system somewhat more secure +by protecting set-user-id (set-group-id) files +from remaining set-user-id (set-group-id) if they are modified, +at the expense of a degree of compatibility. +.Sh RETURN VALUES +.Rv -std +.Sh ERRORS +The +.Fn chmod +system call +will fail and the file mode will be unchanged if: +.Bl -tag -width Er +.It Bq Er ENOTDIR +A component of the path prefix is not a directory. +.It Bq Er ENAMETOOLONG +A component of a pathname exceeded 255 characters, +or an entire path name exceeded 1023 characters. +.It Bq Er ENOENT +The named file does not exist. +.It Bq Er EACCES +Search permission is denied for a component of the path prefix. +.It Bq Er ELOOP +Too many symbolic links were encountered in translating the pathname. +.It Bq Er EPERM +The effective user ID does not match the owner of the file and +the effective user ID is not the super-user. +.It Bq Er EPERM +The effective user ID is not the super-user, the effective user ID do match the +owner of the file, but the group ID of the file does not match the effective +group ID nor one of the supplementary group IDs. +.It Bq Er EPERM +The named file has its immutable or append-only flag set, see the +.Xr chflags 2 +manual page for more information. +.It Bq Er EROFS +The named file resides on a read-only file system. +.It Bq Er EFAULT +The +.Fa path +argument +points outside the process's allocated address space. +.It Bq Er EIO +An I/O error occurred while reading from or writing to the file system. +.It Bq Er EINTEGRITY +Corrupted data was detected while reading from the file system. +.It Bq Er EFTYPE +The effective user ID is not the super-user, the mode includes the sticky bit +.Dv ( S_ISVTX ) , +and path does not refer to a directory. +.El +.Pp +The +.Fn fchmod +system call will fail if: +.Bl -tag -width Er +.It Bq Er EBADF +The descriptor is not valid. +.It Bq Er EINVAL +The +.Fa fd +argument +refers to a socket, not to a file. +.It Bq Er EROFS +The file resides on a read-only file system. +.It Bq Er EIO +An I/O error occurred while reading from or writing to the file system. +.It Bq Er EINTEGRITY +Corrupted data was detected while reading from the file system. +.El +.Pp +In addition to the +.Fn chmod +errors, +.Fn fchmodat +fails if: +.Bl -tag -width Er +.It Bq Er EBADF +The +.Fa path +argument does not specify an absolute path and the +.Fa fd +argument is neither +.Fa AT_FDCWD +nor a valid file descriptor open for searching. +.It Bq Er EINVAL +The value of the +.Fa flag +argument is not valid. +.It Bq Er ENOTDIR +The +.Fa path +argument is not an absolute path and +.Fa fd +is neither +.Dv AT_FDCWD +nor a file descriptor associated with a directory. +.It Bq Er ENOTCAPABLE +.Fa path +is an absolute path, +or contained a ".." component leading to a +directory outside of the directory hierarchy specified by +.Fa fd , +and the process is in capability mode or the +.Dv AT_RESOLVE_BENEATH +flag was specified. +.El +.Sh SEE ALSO +.Xr chmod 1 , +.Xr chflags 2 , +.Xr chown 2 , +.Xr open 2 , +.Xr stat 2 , +.Xr sticky 7 +.Sh STANDARDS +The +.Fn chmod +system call is expected to conform to +.St -p1003.1-90 , +except for the return of +.Er EFTYPE . +The +.Dv S_ISVTX +bit on directories is expected to conform to +.St -susv3 . +The +.Fn fchmodat +system call is expected to conform to +.St -p1003.1-2008 . +.Sh HISTORY +The +.Fn chmod +function appeared in +.At v1 . +The +.Fn fchmod +system call appeared in +.Bx 4.2 . +The +.Fn lchmod +system call appeared in +.Fx 3.0 . +The +.Fn fchmodat +system call appeared in +.Fx 8.0 . |