chroot (BPX1CRT, BPX4CRT) — Change the root directory

Function

The chroot service changes the root directory from the current one to a new one. The root directory is the starting point for path searches of pathnames beginning with a slash. The working directory of the process is unaffected by chroot().

Requirements

Parameters

Pathname_length

Supplied parameter

Type:

Integer

Length:

Fullword

The name of a fullword that contains the length of the pathname of the directory that is to become your root directory.

Pathname

Supplied parameter

Type:

Character string

Character set:

No restriction

Length:

Specified by the Pathname_length parameter

The name of a field that contains the pathname of the new directory. This field has the length that is specified in Pathname_length.

Pathnames can begin with or without a slash:

• A pathname that begins with a slash is an absolute pathname. The slash refers to the current root directory, and the search for the file starts at the current root directory.
• A pathname that does not begin with a slash is a relative pathname. The search for the file starts at the working directory.

Return_value

Returned parameter

Type:

Integer

Length:

Fullword

The name of a fullword in which the chroot service returns 0 if the request is successful, or -1 if it is not successful.

Return_code

Returned parameter

Type:

Integer

Length:

Fullword

The name of a fullword in which the chroot service stores the return code. The chroot service returns Return_code only if Return_value is -1. See z/OS UNIX System Services Messages and Codes for a complete list of possible return code values. The chroot service can return one of the following values in the Return_code parameter:

Return_code	Explanation
EACCES	The calling process does not have permission to search one of the components of Pathname.
EINVAL	The Pathname parameter is not valid; it contains nulls.
ELOOP	A loop exists in symbolic links that were encountered during resolution of the Pathname argument. This error is issued if more than 24 symbolic links are detected in the resolution of Pathname.
ENAMETOOLONG	Pathname is longer than 1023 characters, or a component of Pathname is longer than 255 characters. Name truncation is not supported.
ENOENT	No directory named Pathname was found, or no Pathname was specified. The following reason codes can accompany the return code: JRChdNoEnt and JRQuiescing.
ENOTDIR	Some component of Pathname is not a directory. The following reason code can accompany the return code: JRChdNotDir.
EPERM	The calling process is not a superuser. The following reason code can accompany the return code: JRUserNotPrivileged.

Reason_code

Returned parameter

Type:

Integer

Length:

Fullword

The name of a fullword in which the chroot service stores the reason code. The chroot service returns a Reason_code only if Return_value is -1. Reason_code further qualifies the Return_code value. See z/OS UNIX System Services Messages and Codes for the reason codes.

Usage notes

1. Upon completion of the chroot, the specified directory is now the logical root of the file system for the process. All searches for pathname beginning with slash (/) start from this directory, and all attempts to use dot dot (..) over the root remain in the new root.
2. A new child process inherits a parent's changed root directory.
3. If the current working directory is above the new root, chroot(.) can be used to reset the root directory to equal the current working directory. However, when the current working directory is above the root directory, getcwd() fails with ENOENT return code.

Related services

• chdir (BPX1CHD, BPX4CHD) — Change the working directory
• closedir (BPX1CLD, BPX4CLD) — Close a directory
• getcwd (BPX1GCW, BPX4GCW) — Get the pathname of the working directory
• mkdir (BPX1MKD, BPX4MKD) — Make a directory
• opendir (BPX1OPD, BPX4OPD) — Open a directory
• readdir (BPX1RDD, BPX4RDD) — Read an entry from a directory
• rmdir (BPX1RMD, BPX4RMD) — Remove a directory
• unlink (BPX1UNL, BPX4UNL) — Remove a directory entry

Characteristics and restrictions

To change the root directory, the caller must have appropriate privileges (see Authorization).