CHMOD(2) | NetBSD System Calls Manual | CHMOD(2) |
int
chmod(const char *path, mode_t mode);
int
lchmod(const char *path, mode_t mode);
int
fchmod(int fd, mode_t mode);
#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 /* save swapped text even after use */
If mode ISVTX (the ‘sticky bit') is set on a regular file, it historically meant that the system should save a shareable copy of the program text in the swap area. When applied to commonly used programs like the shell or editor, this would decrease memory usage and startup time. In NetBSD, the sticky bit may still be set on regular files by the super-user, but has no effect. The historical meaning became obsolete in the 1980s with the advent of memory-mapped executables, and is only documented as a matter of historical interest.
If mode 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 information about the properties of the sticky bit, see sticky(7).
Changing the owner of a file turns off the set-user-id and set-group-id bits; writing to 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.
fchmod() will fail if:
January 4, 2009 | NetBSD 5.99 |