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chroot(8) System Manager's Manual chroot(8) NAME chroot - Changes the root directory of a command SYNOPSIS /usr/sbin/chroot directory command DESCRIPTION Only root can use the chroot command. The chroot command changes the root directory from / to the specified directory when the command exe- cutes. (The command specified includes both the command name as well as any arguments.) Consequently, the root of any path (as indicated by the first / (slash) in the pathname) changes to directory and is always relative to the current root. Even if the chroot command is in effect, directory is relative to the current root of the running process. Several programs may not operate properly after chroot executes. You must ensure that all vital files are present in the new root file sys- tem and the relevant pathnames for the files map correctly in the new root file system. For example, the ls -l command fails to give user and group names if the new root file system does not have a copy of the /etc/passwd and /etc/group files. If the /etc/passwd and /etc/group files in the new root file system represent different user and group names, then the output from the ls -l command will be based on those names, not the ones for the system's own name database. Utilities that depend on de- scription files produced by the ctab command may also fail if the re- quired description files are not present in the new root file system. The chroot program uses the execv() function to invoke the specified command. As a consequence, the command specified must be an executable binary, not a shell script. Further, if the program requires indirect loading (for example, due to unresolved symbols requiring use of a shared library), then /sbin/loader as well as any files it requires (for example, shared libraries) must be present in the new root file system in the appropriate locations. EXAMPLES To run a subshell with another file system as the root, enter a command similar to the following. Note in this example, the file system is on the /dev/ra1a device and is mounted to /mnt/ra1a: chroot /mnt/ra1a /sbin/sh The command shown in the previous example specifies a change from the current root file system to the one mounted on /mnt/ra1a while /sbin/sh (which itself is relative to the new root file system) exe- cutes. When /bin/sh executes, the original root file system is inac- cessible. The file system mounted on /mnt/ra1a must contain the stan- dard directories of a root file system. In particular, the shell looks for commands in /sbin, /bin, and /usr/bin (among others) on the new root file system. Running the /sbin/sh command creates a subshell that runs as a separate process from the original shell. Press to exit the subshell and return to the original shell. This restores the environment of the original shell, including the meanings of the current directory (.) and the root directory (/). To run a command in another root file system and save the output on the initial root file system, enter a command similar to the following. Note in this example, the file system is on the /dev/ra1a device and is mounted to /mnt/ra1a: chroot /mnt/ra1a /bin/cc -E /u/bob/prog.c > prep.out The previous command runs the /bin/cc command with /mnt/ra1a as the specified root file system. It compiles the /mnt/ra1a/u/bob/prog.c file, reads the #include files from the /mnt/ra1a/usr/include directory, and puts the compiled text in the prep.out file on the initial root file system. To create a file rela- tive to the original root rather than the new one, use this syntax and enter: chroot directory command > file CAUTIONS If special files in the new root have different major and minor device numbers than the initial root directory, it is possible to overwrite the file system. FILES Specifies the command path. RELATED INFORMATION Commands: cc(1), cpp(1), ls(1), sh(1) Functions: chdir(2), chroot(2) exec(2) delim off chroot(8)