Stand-alone shell
Encyclopedia
Stand-alone shell is a Unix shell
designed for use in recovering from certain types of system failures.
The built in commands of sash have all libraries linked statically, so unlike most shells, the standard UNIX
commands do not rely on external libraries. For example the copy command (cp) requires linux-gate.so, libc.so
, and ld-linux.so
when built from GNU
coreutils on Linux
. If any of these libraries get corrupted, the coreutils cp command would not work, however in sash, the built-in command, cp, would be unaffected.
Sash has the following built-in
commands:
-ar
, -chattr
, -chgrp
, -chmod
, -chown
, -cmp, -cp
, -dd
, -echo, -ed
, exec
, -grep
, -file, -find
, -gunzip, -gzip
, -kill
, -losetup, -ln
, -ls
, -lsattr
, -mkdir
, -mknod, -rmdir
, -sum
, -sync
, -tar
, -touch
, -umount, -where
, -pivot root, and -losetup commands. These functions provide interfaces to the respective Linux system calls. They are especially useful when sash is used in a initial ramdisk ("initrd
") environment. In addition, simple shell variable expansion support has been added. e.g. the variable "$(VAR)" is replaced by the content of the environment variable
"VAR".
Some Linux distros, such as Debian
and Slackware
(via SlackBuilds.org) have this available.
Unix shell
A Unix shell is a command-line interpreter or shell that provides a traditional user interface for the Unix operating system and for Unix-like systems...
designed for use in recovering from certain types of system failures.
The built in commands of sash have all libraries linked statically, so unlike most shells, the standard UNIX
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
commands do not rely on external libraries. For example the copy command (cp) requires linux-gate.so, libc.so
GNU C Library
The GNU C Library, commonly known as glibc, is the C standard library released by the GNU Project. Originally written by the Free Software Foundation for the GNU operating system, the library's development has been overseen by a committee since 2001, with Ulrich Drepper from Red Hat as the lead...
, and ld-linux.so
Strings (Unix)
In computer software, strings is a program in Unix-like operating systems that finds and prints text strings embedded in binary files such as executables.It can be used on object files, and core dumps....
when built from GNU
GNU
GNU is a Unix-like computer operating system developed by the GNU project, ultimately aiming to be a "complete Unix-compatible software system"...
coreutils on Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
. If any of these libraries get corrupted, the coreutils cp command would not work, however in sash, the built-in command, cp, would be unaffected.
Sash has the following built-in
Shell builtin
In computing, a shell builtin is a command or a function, called from a shell, that is executed directly in the shell itself, instead of an external executable program which the shell would load and execute....
commands:
-ar
Ar (Unix)
The archiver is a Unix utility that maintains groups of files as a single archive file. Today, ar is generally used only to create and update static library files that the link editor or linker uses; it can be used to create archives for any purpose, but has been largely replaced by tar for...
, -chattr
Chattr
chattr is a command in the Linux operating system that allows a user to set certain attributes on a file residing on an ext2-based filesystem. chflags is the analogous command on modern BSD systems, including Mac OS X. The commands are similar to the attrib command on DOS, OS/2 and Microsoft Windows...
, -chgrp
Chgrp
The chgrp command is used by unprivileged users on Unix-like systems to change the group associated with a computer file...
, -chmod
Chmod
The chmod command is a Unix command that lets a user tell the system how much access it should permit to a file. It changes the file system modes of files and directories. The modes include permissions and special modes...
, -chown
Chown
The chown command is used on Unix-like systems to change the owner of a file. In most implementations, it can only be executed by the superuser. Unprivileged users who wish to change the group of a file that they own may use chgrp.-Usage examples:These examples illustrate typical syntax and use...
, -cmp, -cp
Cp (Unix)
cp is a UNIX command used to copy a file. Files can be copied either to the same directory or to a completely different directory, possibly on a different file system or hard disk drive. If the file is copied to the same directory, the new file must have a different name to the original; in all...
, -dd
Dd (Unix)
In computing, dd is a common Unix program whose primary purpose is the low-level copying and conversion of raw data. According to the manual page for Version 7 Unix, it will "convert and copy a file". It is used to copy a specified number of bytes or blocks, performing on-the-fly byte order...
, -echo, -ed
Ed (text editor)
ed is a line editor for the Unix operating system. It was one of the first end-user programs hosted on the system and has been standard in Unix-based systems ever since. ed was originally written in PDP-11/20 assembler by Ken Thompson in 1971...
, exec
Exec (operating system)
The exec collection of functions of Unix-like operating systems cause the running process to be completely replaced by the program passed as an argument to the function...
, -grep
Grep
grep is a command-line text-search utility originally written for Unix. The name comes from the ed command g/re/p...
, -file, -find
Find
In Unix-like and some other operating systems, find is a command-line utility that searches through one or more directory trees of a file system, locates files based on some user-specified criteria and applies a user-specified action on each matched file...
, -gunzip, -gzip
Gzip
Gzip is any of several software applications used for file compression and decompression. The term usually refers to the GNU Project's implementation, "gzip" standing for GNU zip. It is based on the DEFLATE algorithm, which is a combination of Lempel-Ziv and Huffman coding...
, -kill
Kill (Unix)
In computing, kill is a command that is used in several popular operating systems to send signals to running processes, for example to request the termination of this process.-Unix and Unix-like:...
, -losetup, -ln
Ln (Unix)
ln is a standard Unix command used to create links to files.- Link files :Links allow more than one file name to refer to the same file, elsewhere.There are two types of links, both of which are created by ln:...
, -ls
Ls
In computing, ls is a command to list files in Unix and Unix-like operating systems. ls is specified by POSIX and the Single UNIX Specification.- History :An ls utility appeared in the original version of AT&T UNIX...
, -lsattr
Lsattr
lsattr is a command-line program for listing the attributes on a Linux second extended file system . It is also a command to display attributes of devices on an AIX operating system.-Options:The form of the lsattr command :...
, -mkdir
Mkdir
The mkdir command in the Unix, DOS, OS/2 and Microsoft Windows operating systems is used to make a new directory. In DOS, OS/2 and Windows the command is often abbreviated to md.-Usage:Normal usage is as straightforward as follows:...
, -mknod, -rmdir
Rmdir
rmdir is a command which will remove an empty directory on a Unix, DOS, OS/2 or Microsoft Windows operating system. In Unix, Linux, and MacOS, it is case sensitive, whereas DOS, OS/2 and Windows , you can type the characters in any combination of upper case and lower case letters, and rd/rmdir...
, -sum
Sum (Unix)
Sum is a core GNU utility written by Kayvan Aghaiepour and David MacKenzie and distributed with the UNIX- and Linux-based operating systems. This utility outputs the checksum of each argument file, as well as the number of blocks they take on disk....
, -sync
Sync (Unix)
sync is a standard system call in the Unix operating system, which commits to disk all data in the kernel filesystem buffers, i.e., data which has been scheduled for writing via low-level I/O system calls. Note that higher-level I/O layers such as stdio may maintain separate buffers of their...
, -tar
Tar (file format)
In computing, tar is both a file format and the name of a program used to handle such files...
, -touch
Touch (Unix)
touch is a standard Unix program used to change a file's access and modification timestamps. It is also used to create a new empty file.- History :A touch utility appeared in Version 7 AT&T UNIX...
, -umount, -where
sash-plus-patches
sash-plus-patches is a collection of patches for sash. The key features are the -chrootChroot
A chroot on Unix operating systems is an operation that changes the apparent root directory for the current running process and its children. A program that is run in such a modified environment cannot name files outside the designated directory tree. The term "chroot" may refer to the chroot...
, -pivot root, and -losetup commands. These functions provide interfaces to the respective Linux system calls. They are especially useful when sash is used in a initial ramdisk ("initrd
Initrd
In computing, initrd is a scheme for loading a temporary file system into memory in the boot process of the Linux kernel. initrd and initramfs refer to slightly different methods of achieving this...
") environment. In addition, simple shell variable expansion support has been added. e.g. the variable "$(VAR)" is replaced by the content of the environment variable
Environment variable
Environment variables are a set of dynamic named values that can affect the way running processes will behave on a computer.They can be said in some sense to create the operating environment in which a process runs...
"VAR".
Some Linux distros, such as Debian
Debian
Debian is a computer operating system composed of software packages released as free and open source software primarily under the GNU General Public License along with other free software licenses. Debian GNU/Linux, which includes the GNU OS tools and Linux kernel, is a popular and influential...
and Slackware
Slackware
Slackware is a free and open source Linux-based operating system. It was one of the earliest operating systems to be built on top of the Linux kernel and is the oldest currently being maintained. Slackware was created by Patrick Volkerding of Slackware Linux, Inc. in 1993...
(via SlackBuilds.org) have this available.