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Stand-alone Shell
Stand-alone shell (sash) is a Unix shell designed for use in recovering from certain types of system failures and errors. The built-in commands of sash have all libraries linked statically, so unlike most shells on Linux, the standard UNIX commands do not rely on external libraries. For example, the copy command (cp) requires libc.so and ld-linux.so when built from GNU Core Utilities 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. In earlier times, most critical commands (including shells) in /sbin or even /bin were statically linked for this purpose, whereas in /usr/sbin and /usr/bin you would find the more feature-rich versions that were dynamically linked. This is not common anymore and as such, statically linked shells with built-in commands have become more important. Sash has the following built-in commands: : ar, chattr, chgrp, chmod, chown, cmp, cp, dd, echo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Screenshot
screenshot (also known as screen capture or screen grab) is a digital image that shows the contents of a computer display. A screenshot is created by the operating system or software running on the device powering the display. Additionally, screenshots can be captured by an external camera, using photography to capture contents on the screen. Screenshot techniques Digital techniques The first screenshots were created with the first interactive computers around 1960. Through the 1980s, computer operating systems did not universally have built-in functionality for capturing screenshots. Sometimes text-only screens could be dumped to a text file, but the result would only capture the content of the screen, not the appearance, nor were graphics screens preservable this way. Some systems had a BSAVE command that could be used to capture the area of memory where screen data was stored, but this required access to a BASIC prompt. Systems with composite video output could be conn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dd (Unix)
dd is a command-line utility for Unix, Plan 9, Inferno, and Unix-like operating systems and beyond, the primary purpose of which is to convert and copy files. On Unix, device drivers for hardware (such as hard disk drives) and special device files (such as /dev/zero and /dev/random) appear in the file system just like normal files; can also read and/or write from/to these files, provided that function is implemented in their respective driver. As a result, can be used for tasks such as backing up the boot sector of a hard drive, and obtaining a fixed amount of random data. The program can also perform conversions on the data as it is copied, including byte order swapping and conversion to and from the ASCII and EBCDIC text encodings. History The name is an allusion to the DD statement found in IBM's Job Control Language (JCL), in which it is an abbreviation for "Data Definition". The command's syntax resembles a JCL statement more than other Unix commands do, so much th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mknod
In Unix-like operating systems, a device file or special file is an interface to a device driver that appears in a file system as if it were an ordinary file. There are also special files in DOS, OS/2, and Windows. These special files allow an application program to interact with a device by using its device driver via standard input/output system calls. Using standard system calls simplifies many programming tasks, and leads to consistent user-space I/O mechanisms regardless of device features and functions. Overview Device files usually provide simple interfaces to standard devices (such as printers and serial ports), but can also be used to access specific unique resources on those devices, such as disk partitions. Additionally, device files are useful for accessing system resources that have no connection with any actual device, such as data sinks and random number generators. There are two general kinds of device files in Unix-like operating systems, known as ''character ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mkdir
The mkdir (make directory) command in the Unix, DOS, DR FlexOS, IBM OS/2, Microsoft Windows, and ReactOS operating systems is used to make a new directory. It is also available in the EFI shell and in the PHP scripting language. In DOS, OS/2, Windows and ReactOS, the command is often abbreviated to md. The command is analogous to the Stratus OpenVOS create_dir command. MetaComCo TRIPOS and AmigaDOS provide a similar MakeDir command to create new directories. The numerical computing environments MATLAB and GNU Octave include an mkdir function with similar functionality. History In early versions of Unix ( 4.1BSD and early versions of System V), this command had to be setuid root as the kernel did not have an mkdir syscall. Instead, it made the directory with mknod and linked in the . and .. directory entries manually. The command is available in MS-DOS versions 2 and later. Digital Research DR DOS 6.0 and Datalight ROM-DOS also include an implementation of the and comma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ln (Unix)
The command is a standard Unix command utility used to create a hard link or a symbolic link (symlink) to an existing file or directory. The use of a hard link allows multiple filenames to be associated with the same file since a hard link points to the inode of a given file, the data of which is stored on disk. On the other hand, symbolic links are special files that refer to other files by name. The command by default creates hard links, and when called with the command line parameter creates symbolic links. Most operating systems prevent hard links to directories from being created since such a capability could disrupt the structure of a file system and interfere with the operation of other utilities. The command can however be used to create symbolic links to non-existent files. History ln appeared in Issue 2 of the X/Open Portability Guidelines. The version of bundled in GNU coreutils was written by Mike Parker and David MacKenzie. The command is available as a separate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Losetup
In Unix-like operating systems, a loop device, vnd (vnode disk), or lofi (loop file interface) is a pseudo-device that makes a computer file accessible as a block device. Before use, a loop device must be connected to an extant file in the file system. The association provides the user with an application programming interface (API) that allows the file to be used in place of a block special file (cf. device file system). Thus, if the file contains an entire file system, the file may then be mounted as if it were a disk device. Files of this kind are often used for CD ISO images and floppy disk images. Mounting a file containing a file system via such a loop mount makes the files within that file system accessible. They appear in the mount point directory. A loop device may allow some kind of data elaboration during this redirection. For example, the device may be the unencrypted version of an encrypted file. In such a case, the file associated with a loop device may be another pse ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kill (command)
In computing, kill is a command that is used in several popular operating systems to send signals to running processes. Implementations Unix and Unix-like In Unix and Unix-like operating systems, kill is a command used to send a signal to a process. By default, the message sent is the termination signal, which requests that the process exit. But ''kill'' is something of a misnomer; the signal sent may have nothing to do with process killing. The kill command is a wrapper around the kill() system call, which sends signals to processes or process groups on the system, referenced by their numeric process IDs (PIDs) or process group IDs (PGIDs). kill is always provided as a standalone utility as defined by the POSIX standard. However, most shells have built-in kill commands that may slightly differ from it. There are many different signals that can be sent (see ''signal'' for a full list), although the signals in which users are generally most interested are SIGTERM ("termina ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gzip
gzip is a file format and a software application used for file compression and decompression. The program was created by Jean-loup Gailly and Mark Adler as a free software replacement for the compress program used in early Unix systems, and intended for use by GNU (from where the "g" of gzip is derived). Version 0.1 was first publicly released on 31 October 1992, and version 1.0 followed in February 1993. The decompression of the ''gzip'' format can be implemented as a streaming algorithm, an important feature for Web protocols, data interchange and ETL (in standard pipes) applications. File format gzip is based on the DEFLATE algorithm, which is a combination of LZ77 and Huffman coding. DEFLATE was intended as a replacement for LZW and other patent-encumbered data compression algorithms which, at the time, limited the usability of compress and other popular archivers. "gzip" is often also used to refer to the gzip file format, which is: * a 10-byte header, contai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Find (Unix)
In Unix-like and some other operating systems, find is a command-line utility that locates files based on some user-specified criteria and either prints the pathname of each matched object or, if another action is requested, performs that action on each matched object. It initiates a search from a desired starting location and then recursively traverses the nodes (directories) of a hierarchical structure (typically a tree). find can traverse and search through different file systems of partitions belonging to one or more storage devices mounted under the starting directory. The possible search criteria include a pattern to match against the filename or a time range to match against the modification time or access time of the file. By default, find returns a list of all files below the current working directory, although users can limit the search to any desired maximum number of levels under the starting directory. The related locate programs use a database of indexed files ob ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File (command)
The file command is a standard program of Unix and Unix-like operating systems for recognizing the type of data contained in a computer file. History The original version of file originated in Unix Research Version 4 in 1973. System V brought a major update with several important changes, most notably moving the file type information into an external text file rather than compiling it into the binary itself. Most major BSD and Linux distributions use a free, open-source reimplementation which was written in 1986–87 by Ian Darwin from scratch. It was expanded by Geoff Collyer in 1989 and since then has had input from many others, including Guy Harris, Chris Lowth and Eric Fischer; from late 1993 onward its maintenance has been organized by Christos Zoulas. The OpenBSD system has its own subset implementation written from scratch, but still uses the Darwin/Zoulas collection of magic file formatted information. The command has also been ported to the IBM i operating system. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grep
grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Its name comes from the ed command ''g/re/p'' (''globally search for a regular expression and print matching lines''), which has the same effect. grep was originally developed for the Unix operating system, but later available for all Unix-like systems and some others such as OS-9. History Before it was named, grep was a private utility written by Ken Thompson to search files for certain patterns. Doug McIlroy, unaware of its existence, asked Thompson to write such a program. Responding that he would think about such a utility overnight, Thompson actually corrected bugs and made improvements for about an hour on his own program called s (short for "search"). The next day he presented the program to McIlroy, who said it was exactly what he wanted. Thompson's account may explain the belief that grep was written overnight. Thompson wrote the first version in PDP-11 assembly ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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