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28 .Dd September 29, 2020
33 .Nd change root directory
39 .Fn chroot "const char *dirname"
44 is the address of the pathname of a directory, terminated by an ASCII NUL.
49 to become the root directory,
50 that is, the starting point for path searches of pathnames
54 In order for a directory to become the root directory
55 a process must have execute (search) access for that directory.
57 It should be noted that
59 has no effect on the process's current directory.
61 This call is restricted to the super-user.
63 Depending on the setting of the
64 .Ql kern.chroot_allow_open_directories
65 sysctl variable, open filedescriptors which reference directories
71 .Ql kern.chroot_allow_open_directories
76 if there are any directories open.
79 .Ql kern.chroot_allow_open_directories
80 is set to one (the default),
84 if there are any directories open and the
85 process is already subject to the
90 .Ql kern.chroot_allow_open_directories
91 will bypass the check for open directories,
92 mimicking the historic insecure behavior of
94 still present on other systems.
101 will fail and the root directory will be unchanged if:
104 A component of the path name is not a directory.
106 The effective user ID is not the super-user, or one or more
107 filedescriptors are open directories.
108 .It Bq Er ENAMETOOLONG
109 A component of a pathname exceeded 255 characters,
110 or an entire path name exceeded 1023 characters.
112 The named directory does not exist.
114 Search permission is denied for any component of the path name.
116 Too many symbolic links were encountered in translating the pathname.
121 points outside the process's allocated address space.
123 An I/O error occurred while reading from or writing to the file system.
125 Corrupted data was detected while reading from the file system.
133 system call appeared in
139 and was removed in subsequent standards.
141 If the process is able to change its working directory to the target
142 directory, but another access control check fails (such as a check for
143 open directories, or a MAC check), it is possible that this system
144 call may return an error, with the working directory of the process
146 .Sh SECURITY CONSIDERATIONS
147 The system has many hardcoded paths to files which it may load after
149 It is generally recommended to drop privileges immediately after a
153 and restrict write access to a limited subtree of the
157 setup the sandbox so that the sandboxed user will have no write
158 access to any well-known system directories.
160 For complete isolation from the rest of the system, use