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Fsync
sync is a standard system call in the Unix operating system, which commits all data in the kernel filesystem to non-volatile storage buffers, i.e., data which has been scheduled for writing via low-level I/O system calls. Higher-level I/O layers such as stdio may maintain separate buffers of their own. As a function in C, the sync() call is typically declared as void sync(void) in . The system call is also available via a command line utility also called ''sync'', and similarly named functions in other languages such as Perl and Node.js (in the fs module). The related system call fsync() commits just the buffered data relating to a specified file descriptor. fdatasync() is also available to write out just the changes made to the data in the file, and not necessarily the file's related metadata. Some Unix systems run a kind of ''flush'' or ''update'' daemon, which calls the ''sync'' function on a regular basis. On some systems, the cron daemon does this, and on Linux it wa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Native Command Queuing
In computing, Native Command Queuing (NCQ) is an extension of the Serial ATA protocol allowing hard disk drives to internally optimize the order in which received read and write commands are executed. This can reduce the amount of unnecessary drive head movement, resulting in increased performance (and slightly decreased wear of the drive) for workloads where multiple simultaneous read/write requests are outstanding, most often occurring in server-type applications. History Native Command Queuing was preceded by Parallel ATA's version of Tagged Command Queuing (TCQ). ATA's attempt at integrating TCQ was constrained by the requirement that ATA host bus adapters use ISA bus device protocols to interact with the operating system. The resulting high CPU overhead and negligible performance gain contributed to a lack of market acceptance for TCQ. NCQ differs from TCQ in that, with NCQ, each command is of equal importance, but NCQ's host bus adapter also programs its own first part ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File Descriptor
In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier ( handle) for a file or other input/output resource, such as a pipe or network socket. File descriptors typically have non-negative integer values, with negative values being reserved to indicate "no value" or error conditions. File descriptors are a part of the POSIX API. Each Unix process (except perhaps daemons) should have three standard POSIX file descriptors, corresponding to the three standard streams: Overview In the traditional implementation of Unix, file descriptors index into a per-process maintained by the kernel, that in turn indexes into a system-wide table of files opened by all processes, called the . This table records the ''mode'' with which the file (or other resource) has been opened: for reading, writing, appending, and possibly other modes. It also indexes into a third table called the inode table that describes the ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
System Call
In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, accessing a hard disk drive or accessing the device's camera), creation and execution of new processes, and communication with integral kernel services such as process scheduling. System calls provide an essential interface between a process and the operating system. In most systems, system calls can only be made from userspace processes, while in some systems, OS/360 and successors for example, privileged system code also issues system calls. Privileges The architecture of most modern processors, with the exception of some embedded systems, involves a security model. For example, the '' rings'' model specifies multiple privilege levels under which software may be executed: a program is usually limited to its own address space so that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File System Permissions
Most file systems include attributes of files and directories that control the ability of users to read, change, navigate, and execute the contents of the file system. In some cases, menu options or functions may be made visible or hidden depending on a user's permission level; this kind of user interface is referred to as permission-driven. Two types of permissions are widely available: traditional Unix file system permissions and access-control lists (ACLs) which are capable of more specific control. File system variations The original File Allocation Table file system has a per-file all-user read-only attribute. NTFS implemented in Microsoft Windows NT and its derivatives, use ACLs to provide a complex set of permissions. OpenVMS uses a permission scheme similar to that of Unix. There are four categories (system, owner, group, and world) and four types of access permissions (Read, Write, Execute and Delete). The categories are not mutually disjoint: World includes Group ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SATA
SATA (Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard to become the predominant interface for storage devices. Serial ATA industry compatibility specifications originate from the Serial ATA International Organization (SATA-IO) which are then promulgated by the INCITS Technical Committee T13, AT Attachment (INCITS T13). History SATA was announced in 2000 in order to provide several advantages over the earlier PATA interface such as reduced cable size and cost (seven conductors instead of 40 or 80), native hot swapping, faster data transfer through higher signaling rates, and more efficient transfer through an (optional) I/O queuing protocol. Revision 1.0 of the specification was released in January 2003. Serial ATA industry compatibility specifications originate from the Serial ATA Int ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SCSI
Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interfaces. The SCSI standard defines command sets for specific peripheral device types; the presence of "unknown" as one of these types means that in theory it can be used as an interface to almost any device, but the standard is highly pragmatic and addressed toward commercial requirements. The initial Parallel SCSI was most commonly used for hard disk drives and tape drives, but it can connect a wide range of other devices, including scanners and CD drives, although not all controllers can handle all devices. The ancestral SCSI standard, X3.131-1986, generally referred to as SCSI-1, was published by the X3T9 technical committee of the American National Standards Institute (ANSI) in 1986. SCSI-2 was published in August 1990 as X3.T9.2/86-109 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
FreeBSD
FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular open-source BSD operating system, accounting for more than three-quarters of all installed and permissively licensed BSD systems. FreeBSD has similarities with Linux, with two major differences in scope and licensing: FreeBSD maintains a complete system, i.e. the project delivers a kernel, device drivers, userland utilities, and documentation, as opposed to Linux only delivering a kernel and drivers, and relying on third-parties for system software; FreeBSD source code is generally released under a permissive BSD license, as opposed to the copyleft GPL used by Linux. The FreeBSD project includes a security team overseeing all software shipped in the base distribution. A wide range of additional third-party applications may be i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hdparm
hdparm is a command line program for Linux to set and view ATA hard disk drive hardware parameters and test performance. It can set parameters such as drive caches, sleep mode, power management, acoustic management, and DMA settings. GParted and Parted Magic both include ''hdparm''. Changing hardware parameters from suboptimal conservative defaults to their optimal settings can improve performance greatly. For example, turning on DMA can, in some instances, double or triple data throughput. There is, however, no reliable method for determining the optimal settings for a given controller-drive combination, except careful trial and error. Depending on the given parameters, ''hdparm'' can cause computer crashes or render the data on the disk inaccessible. Usage examples hdparm has to be run with special privileges, otherwise it will either not be found or the requested actions will not be executed properly. Display information of the hard drive: sudo hdparm -I /dev/sda T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Page Cache
In computing, a page cache, sometimes also called disk cache, is a transparent cache for the pages originating from a secondary storage device such as a hard disk drive (HDD) or a solid-state drive (SSD). The operating system keeps a page cache in otherwise unused portions of the main memory (RAM), resulting in quicker access to the contents of cached pages and overall performance improvements. A page cache is implemented in kernels with the paging memory management, and is mostly transparent to applications. Usually, all physical memory not directly allocated to applications is used by the operating system for the page cache. Since the memory would otherwise be idle and is easily reclaimed when applications request it, there is generally no associated performance penalty and the operating system might even report such memory as "free" or "available". When compared to main memory, hard disk drive read/writes are slow and random accesses require expensive disk seeks; as a resul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fflush
The C programming language provides many standard library functions for file input and output. These functions make up the bulk of the C standard library header . The functionality descends from a "portable I/O package" written by Mike Lesk at Bell Labs in the early 1970s, and officially became part of the Unix operating system in Version 7. The I/O functionality of C is fairly low-level by modern standards; C abstracts all file operations into operations on streams of bytes, which may be "input streams" or "output streams". Unlike some earlier programming languages, C has no direct support for random-access data files; to read from a record in the middle of a file, the programmer must create a stream, seek to the middle of the file, and then read bytes in sequence from the stream. The stream model of file I/O was popularized by Unix, which was developed concurrently with the C programming language itself. The vast majority of modern operating systems have inherited streams ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Write()
The write is one of the most basic routines provided by a Unix-like operating system kernel. It writes data from a buffer declared by the user to a given device, such as a file. This is the primary way to output data from a program by directly using a system call. The destination is identified by a numeric code. The data to be written, for instance a piece of text, is defined by a pointer and a size, given in number of bytes. write thus takes three arguments: # The file code (file descriptor or fd). # The pointer to a buffer where the data is stored (buf). # The number of bytes to write from the buffer (nbytes). POSIX usage The write call interface is standardized by the POSIX specification. Data is written to a file by calling the write function. The function prototype is: ssize_t write(int fd, const void *buf, size_t nbytes); In above syntax, ssize_t is a typedef. It is a signed data type defined in stddef.h. Note that write() does not return an unsigned value; it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
