Unix жүйесіндегі 'rm' командасы: файлдарды жою туралы ақпарат

Unix command utility

rm (short for remove) is a basic command on Unix and Unix like operating systems used to remove objects such as computer files, directories and symbolic links from file systems and also special files such as device nodes, pipes and sockets, similar to the del command in MS DOS, OS/2, and Microsoft Windows. The command is also available in the EFI shell.

The rm command removes references to objects from the filesystem using the unlink system call, where those objects might have had multiple references (for example, a file with two different names), and the objects themselves are discarded only when all references have been removed and no programs still have open handles to the objects. This allows for scenarios where a program can open a file, immediately remove it from the filesystem, and then use it for temporary space, knowing that the file's space will be reclaimed after the program exits, even if it exits by crashing. The command generally does not destroy file data, since its purpose is really merely to unlink references, and the filesystem space freed may still contain leftover data from the removed file. This can be a security concern in some cases, and hardened versions sometimes provide for wiping out the data as the last link is being cut, and programs such as shred and srm are available which specifically provide data wiping capability. rm is generally only seen on UNIX derived operating systems, which typically do not provide for recovery of deleted files through a mechanism like the recycle bin, hence the tendency for users to enclose rm in some kind of wrapper to limit accidental file deletion. There are undelete utilities that will attempt to reconstruct the index and can bring the file back if the parts were not reused.

On some old versions of Unix, the rm command would delete directories if they were empty. This behaviour can still be obtained in some versions of rm with the d flag, e. g., the BSDs (such as FreeBSD, NetBSD, OpenBSD and macOS) derived from 4.4BSD Lite2. The version of rm bundled in GNU coreutils was written by Paul Rubin, David MacKenzie, Richard Stallman, and Jim Meyering. This version also provides d option, to help with compatibility. The same functionality is provided by the standard rmdir command. The i option in Version 7 replaced dsw, or "delete from switches", which debuted in Version 1. Doug McIlroy wrote that dsw "was a desperation tool designed to clean up files with unutterable names". The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix like utilities. KolibriOS includes an implementation of the command. The command has also been ported to the IBM i operating system.

Usually, on most filesystems, deleting a file requires write permission on the parent directory (and execute permission, in order to enter the directory in the first place). (Note that, confusingly for beginners, permissions on the file itself are irrelevant. However, GNU rm asks for confirmation if a write protected file is to be deleted, unless the f option is used.) To delete a directory (with rm r), one must delete all of its contents recursively. This requires that one must have read and write and execute permission to that directory (if it's not empty) and all non empty subdirectories recursively (if there are any). The read permissions are needed to list the contents of the directory in order to delete them. This sometimes leads to an odd situation where a non empty directory cannot be deleted because one doesn't have write permission to it and so cannot delete its contents; but if the same directory were empty, one would be able to delete it. If a file resides in a directory with the sticky bit set, then deleting the file requires one to be the owner of the file.

Sun Microsystems introduced "rm rf /" protection in Solaris 10, first released in 2005. Upon executing the command, the system now reports that the removal of / is not allowed. Shortly after, the same functionality was introduced into FreeBSD version of rm utility. GNU rm refuses to execute rm rf / if the preserve root option is given, which has been the default since version 6.4 of GNU Core Utilities was released in 2006. In newer systems, this failsafe is always active, even without the option. To run the command, user must bypass the failsafe by adding the option no preserve root, even if they are the superuser.

GNU Core Utilities implementation used in multiple Linux distributions will be limited in command line arguments bytes number of pages that are allocated within the kernel for command line arguments before kernel 2.6.23 Released on 9 October 2007 were defined at kernel compile time at variable MAX ARG PAGES in include/linux/binfmts. h file but new kernels limits the maximum argument length to 25% of the maximum stack limit (ulimit s). Error: /bin/rm: Argument list too long. will prompt if command line argument limit is exceed