$ sudo /usr/sbin/chroot /tmp/jail /bin/bash in .NET Integrating ean13+2 in .NET $ sudo /usr/sbin/chroot /tmp/jail /bin/bash

$ sudo /usr/sbin/chroot /tmp/jail /bin/bash use none none creation toreceive none for none Android To set up a none none useful chroot jail, first determine which utilities the users of the chroot jail need. Then copy the appropriate binaries and their libraries into the jail. Alternatively, you can build static copies of the binaries and put them in the jail without installing separate libraries.

(The statically linked binaries are considerably larger than their dynamic counterparts. The size of the base system with bash and the core utilities exceeds 50 megabytes.) You can find the source code for most common utilities in the bash and coreutils source packages.

The chroot utility fails unless you run it with root privileges the preceding examples used sudo to gain these privileges. The result of running chroot with root privileges is a root shell (a shell with root privileges) running inside a chroot jail. Because a user with root privileges can break out of a chroot jail, it is imperative that you run a program in the chroot jail with reduced privileges (i.

e., privileges other than those of root). There are several ways to reduce the privileges of a user.

For example, you can put su or sudo in the jail and then start a shell or a daemon inside the jail, using one of these programs to reduce the privileges of the user working in the jail. A command such as the following starts a shell with reduced privileges inside the jail:. $ sudo /usr /sbin/chroot jailpath /usr/bin/sudo -u user /bin/bash &. where jailp none none ath is the pathname of the jail directory, and user is the username under whose privileges the shell runs. The problem with this scenario is that sudo and su, as compiled for Ubuntu, call PAM. To run one of these utilities you need to put all of PAM, including its libraries and configuration files, in the jail, along with sudo (or su) and the /etc/passwd file.

Alternatively, you can recompile su or sudo. The source code calls PAM, however, so you would need to modify the source so it does not call PAM. Either one of these techniques is time-consuming and introduces complexities that can lead to an insecure jail.

The following C program1 runs a program with reduced privileges in a chroot jail. Because this program obtains the UID and GID of the user you specify on the command line before calling chroot(), you do not need to put /etc/passwd in the jail..

1. Thanks to David Chisnall and the toil Project ( for the uchroot.c program. Setting Up a Server The program reduces the privileges of the specified program to those of the specified user. This program is presented as a simple solution to the preceding issues so you can experiment with a chroot jail and better understand how it works..

$ cat uchro none none ot.c /* See svn.gna.

org/viewcvs/etoile/trunk/Etoile/LiveCD/uchroot.c for terms of use. #include <stdio.

h> #include <stdlib.h> #include <pwd.h> int main(int argc, char * argv[]) { if(argc < 4) { printf("Usage: %s {username} {directory} {program} [arguments]\n", argv[0]); return 1; } /* Parse arguments */ struct passwd * pass = getpwnam(argv[1]); if(pass == NULL) { printf("Unknown user %s\n", argv[1]); return 2; } /* Set the required UID */ chdir(argv[2]); if(chroot(argv[2]) .

setgid(pass->pw_gid) . setuid(pas none for none s->pw_uid)) { printf("%s must be run as root. Current uid=%d, euid=%d\n", argv[0], (int)getuid(), (int)geteuid() ); return 3; } char buf[100]; return execv(argv[3], argv + 3); }. The first o f the following commands compiles uchroot.c, creating an executable file named uchroot. Subsequent commands move uchroot to /usr/local/bin and give it appropriate ownership.

. $ cc -o uch none none root uchroot.c $ sudo mv uchroot /usr/local/bin $ sudo chown root:root /usr/local/bin/uchroot $ ls -l /usr/local/bin/uchroot -rwxr-xr-x 1 root root 7922 2010-07-17 08:26 /usr/local/bin/uchroot. 470 11 System Administration: Core Concepts Using the s none none etup from earlier in this section, give the following command to run a shell with the privileges of the user sam inside a chroot jail:.
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