chroot means ch is root. ch is Child (child process). chroot was introduced in 1979. Here are examples of chroot Command through examples. The reader should know the basics of UNIX, Linux, Unix Shell or Shell, UNIX Wheel Group etc. topics. chroot stands for “ch is root” as said before and is a function under *nix systems to the root directory. It affects only the current process and its child processes. Chroot itself can refer to the system call related to chroot as well as the utility named chroot.
Know The Basics Before Running chroot Command Examples
A program that is “rooted” in a directory and has no open file descriptors in the area outside the virtual root directory, can (with correct implementation of the operating system kernel) no longer access files outside this directory. Chroot thus offers an easy way to untrusted, test or otherwise hazardous programs inside a sandbox. It is a simple Jail mechanism, but from quite easily be broken again.
chroot was not designed as a safety feature, but primarily used for setting up virtual environments. The first known use was greater in Network Software Engineering (NSE) on SunOS in 1986, where a departure from the surroundings was fchroot(1) possible and documented.
In practice, “chrooting” is difficult because programs expect at launch, space for temporary files, configuration files, device files and program libraries to be found at certain fixed locations. To run these programs inside the chroot directory, the directory containing these files needed to be equipped.
Under Linux chroot is not designated as a safety feature. Manual is in the chroot(2) man page documents. Many BSD systems, however, runs a process that needs a chroot environment. FreeBSD provides the concept of jails to foreclose processes from each other. On OS X, you will get manual of chroot by running simple command like GNU Linux – man chroot. There is no /root visible under OS X when used in normal way.
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chroot Command Examples : When We Use
OpenVZ is a virtualization solution that works similar to chroot concept. Since most Unix systems are not completely file system-oriented, potentially dangerous functions such as the control over network and processes can take place through system calls to a chromed program. We use chroot for :
- Privilege Separation : A chroot can be used as a precautionary measure against a breach of security by preventing a potential attacker from inflicting damage with a compromised program or to explore the system.
- Honeypot : A chroot directory can be equipped so that a real system with network services is simulated.
- Testing : The achieved chroot mechanism isolation is also useful for testing purposes. A directory can have its own copy of the operating system as a test environment for softwares whose use would be too risky in a production system.
- Repair : To repair a Linux / Unix system.
- Installing an operating system : The installation of some Linux distributions is only possible via the command line. Therefore, it is necessary to enter after unzipping the distribution archive into a new partition with chroot the new system environment.
chroot Command Examples
Method to chroot (from any live session) to #! on disk via SSH for recovery (done when #! is installed on /dev/sda1 but is not accessible via grub on deb based system) :
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 | sudo su TARGET=/media/sda1 mkdir -p $TARGET mount /dev/sda1 $TARGET mount --bind /dev $TARGET/dev mount --bind /dev/pts $TARGET/dev/pts mount --bind /proc $TARGET/proc mount --bind /sys $TARGET/sys cp /etc/resolv.conf $TARGET/etc/ chroot $TARGET /bin/bash # install grub grub-install /dev/sda update-grub # exits chroot env control-D # unmount umount -l $TARGET/dev/pts umount -l $TARGET/dev umount -l $TARGET/proc umount -l $TARGET/sys # workarounds ## Reboot into the #! system on disk ### Replacing like '/usr/bin/bash' by '/bin/bash' ### cp /etc/resolv.conf into the chroot to make apt-get usable ### source - crunchbang.org |
Basic chroot usage example for nginx chroot ( Partial )
Usage syntax :
1 | chroot [options] /path/to/new/root /path/to/server |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | # J is just a name J=/nginx mkdir -p $J mkdir -p $J/etc mkdir -p $J/dev mkdir -p $J/var mkdir -p $J/usr mkdir -p $J/usr/local/nginx mkdir -p $J/tmp chmod 1777 $J/tmp mkdir -p $J/var/tmp chmod 1777 $J/var/tmp mkdir -p $J/lib64 # tested on rackspace ls -l /dev/{null,random,urandom} # mknod command usage is shown here for the full operation /bin/mknod -m 0666 $J/dev/null c 1 3 /bin/mknod -m 0666 $J/dev/random c 1 8 /bin/mknod -m 0444 $J/dev/urandom c 1 9 # copy /bin/cp -farv /usr/local/nginx/* $J/usr/local/nginx # install dependencies ldd /usr/local/nginx/sbin/nginx # will show huge output # copy all to J |
OS X chroot example
1 2 3 4 5 6 7 8 9 10 11 | # see docs for os x 10.9 at # https://developer.apple.com/library/mac/documentation/Darwin/Reference/Manpages/man8/chroot.8.html # man chroot hdiutil create -fs HFS+ -size 8g -type SPARSE -volname osx-chroot ${CHROOTDIR} hdiutil attach -mountpoint ${CHROOTDIR} ${CHROOTDIR}.sparseimage # attach a DVD image or the real path hdiutil attach -mountpoint /Volumes/osx-install /path/to/dvd # Install packages of your choice # Unmount hdiutil detach ${CHROOTDIR} hdiutil detach /Volumes/osx-install |
This is all as basic about chroot!
