File system calls
The file is the most basic and fundamental abstraction in Linux. Linux follows the everything-is-a-file philosophy. Consequently, much interaction transpires via filesystem system calls such as reading of and writing to files, even when the object in question is not what you would consider your everyday file.
In order to be accessed, a file must first be opened. Files can be opened for reading, writing, or both. An open file is referenced via a unique descriptor, a mapping from the metadata associated with the open file back to the specific file itself. Inside the Linux kernel, this descriptor is handled by an integer (of the C type int) called the file descriptor, abbreviated fd. File descriptors are shared with user space, and are used directly by user programs to access files. A large part of Linux system programming consists of opening, manipulating, closing, and otherwise using file descriptors.
Contents
Tip: For detailed information about each system call please read: Linux man pages
File operations
| Syscall | Number | Description |
|---|---|---|
| CLOSE | 3 | Close a file descriptor |
| CREAT | 85 | Open and possibly create a file |
| OPEN | 2 | Open and possibly create a file |
| OPENAT | 257 | Open and possibly create a file relative to a directory file descriptor |
| NAME_TO_HANDLE_AT | 303 | Obtain handle for a pathname |
| OPEN_BY_HANDLE_AT | 304 | Open file via a handle |
| MEMFD_CREATE | 319 | Сreate an anonymous file |
| MKNOD | 133 | Create a special or ordinary file |
| MKNODAT | 259 | Create a special or ordinary file relative to a directory file descriptor |
| RENAME | 82 | Rename a file |
| RENAMEAT | 264 | Rename a file relative to directory file descriptors |
| RENAMEAT | 316 | Rename a file relative to directory file descriptors |
| TRUNCATE | 76 | Truncate a file to a specified length |
| FTRUNCATE | 77 | Truncate a file to a specified length |
| FALLOCATE | 285 | Manipulate file space |
Directory operations
| Syscall | Number | Description |
|---|---|---|
| MKDIR | 83 | Create a directory |
| MKDIRAT | 258 | Create a directory relative to a directory file descriptor |
| RMDIR | 84 | Delete a directory |
| GETCWD | 79 | Get current working directory |
| CHDIR | 80 | Change working directory |
| FCHDIR | 81 | Change working directory |
| CHROOT | 161 | Change root directory |
| GETDENTS | 78 | Get directory entries |
| GETDENTS64 | 217 | Get directory entries |
| LOOKUP_DCOOKIE | 212 | Return a directory entry's path |
Link operations
| Syscall | Number | Description |
|---|---|---|
| LINK | 86 | Create a hard link to a file |
| LINKAT | 265 | Create a hard link to a file relative to directory file descriptors |
| SYMLINK | 88 | Create a symbolic link to a file |
| SYMLINKAT | 266 | Create a symbolic link to a file relative to a directory file descriptor |
| UNLINK | 87 | Delete a name and possibly the file it refers to |
| UNLINKAT | 263 | Delete a name and possibly the file it refers to relative to a directory file descriptor |
| READLINK | 89 | Read value of a symbolic link |
| READLINKAT | 267 | Read value of a symbolic link relative to a directory file descriptor |
Basic file attributes
| Syscall | Number | Description |
|---|---|---|
| UMASK | 95 | Set file mode creation mask |
| STAT | 4 | Get file metadata |
| LSTAT | 6 | Get link metadata |
| FSTAT | 5 | Get file metadata |
| FSTATAT | 262 | Get file metadata relative to a directory file descriptor |
| CHMOD | 90 | Change permissions of a file |
| FCHMOD | 91 | Change permissions of a file |
| FCHMODAT | 268 | Change permissions of a file relative to a directory file descriptor |
| CHOWN | 92 | Change ownership of a file |
| LCHOWN | 94 | Change ownership of a link |
| FCHOWN | 93 | Change ownership of a file |
| FCHOWNAT | 260 | Change ownership of a file relative to a directory file descriptor |
| UTIME | 132 | Change file last access and modification times |
| UTIMES | 235 | Change file last access and modification times |
| FUTIMESAT | 261 | Change timestamps of a file relative to a directory file descriptor |
| UTIMENSAT | 280 | Change file timestamps with nanosecond precision |
| ACCESS | 21 | Check real user's permissions for a file |
| FACCESSAT | 269 | Check real user's permissions for a file relative to a directory file descriptor |
Extended file attributes
| Syscall | Number | Description |
|---|---|---|
| SETXATTR | 188 | Set an extended attribute value |
| LSETXATTR | 189 | Set an extended attribute value |
| FSETXATTR | 190 | Set an extended attribute value |
| GETXATTR | 191 | Retrieve an extended attribute value |
| LGETXATTR | 192 | Retrieve an extended attribute value |
| FGETXATTR | 193 | Retrieve an extended attribute value |
| LISTXATTR | 194 | List extended attribute names |
| LLISTXATTR | 195 | List extended attribute names |
| FLISTXATTR | 196 | List extended attribute names |
| REMOVEXATTR | 197 | Remove an extended attribute |
| LREMOVEXATTR | 198 | Remove an extended attribute |
| FREMOVEXATTR | 199 | Remove an extended attribute |
File descriptor manipulations
| Syscall | Number | Description |
|---|---|---|
| IOCTL | 16 | Control device |
| FCNTL | 72 | Manipulate file descriptor |
| DUP | 32 | Duplicate a file descriptor |
| DUP2 | 33 | Duplicate a file descriptor |
| DUP3 | 292 | Duplicate a file descriptor |
| FLOCK | 73 | Apply or remove an advisory lock on an open file |
Read/Write
| Syscall | Number | Description |
|---|---|---|
| READ | 0 | Read from a file descriptor |
| READV | 19 | Read data into multiple buffers |
| PREAD | 17 | Read from a file descriptor at a given offset |
| PREADV | 295 | Read data into multiple buffers |
| WRITE | 1 | Write to a file descriptor |
| WRITEV | 20 | Write data into multiple buffers |
| PWRITE | 18 | Write to a file descriptor at a given offset |
| PWRITEV | 296 | Write data into multiple buffers |
| LSEEK | 8 | Reposition read/write file offset |
| SENDFILE | 40 | Transfer data between file descriptors |
Synchronized I/O
| Syscall | Number | Description |
|---|---|---|
| FDATASYNC | 75 | Synchronize a file's in-core state with storage device |
| FSYNC | 74 | Synchronize a file's in-core state with storage device |
| MSYNC | 26 | Synchronize a file with a memory map |
| SYNC_FILE_RANGE | 277 | Sync a file segment with disk |
| SYNC | 162 | Commit buffer cache to disk |
| SYNCFS | 306 | Commit buffer cache to disk |
Asynchronous I/O
| Syscall | Number | Description |
|---|---|---|
| IO_SETUP | 206 | Create an asynchronous I/O context |
| IO_DESTROY | 207 | Destroy an asynchronous I/O context |
| IO_SUBMIT | 209 | Submit asynchronous I/O blocks for processing |
| IO_CANCEL | 210 | Cancel an outstanding asynchronous I/O operation |
| IO_GETEVENTS | 208 | Read asynchronous I/O events from the completion queue |
Multiplexed I/O
| Syscall | Number | Description |
|---|---|---|
| SELECT | 23 | Synchronous I/O multiplexing |
| PSELECT6 | 270 | Synchronous I/O multiplexing |
| POLL | 7 | Wait for some event on a file descriptor |
| PPOLL | 271 | Wait for some event on a file descriptor |
| EPOLL_CREATE | 213 | Open an epoll file descriptor |
| EPOLL_CREATE1 | 291 | Open an epoll file descriptor |
| EPOLL_CTL | 233 | Control interface for an epoll descriptor |
| EPOLL_WAIT | 232 | Wait for an I/O event on an epoll file descriptor |
| EPOLL_PWAIT | 281 | Wait for an I/O event on an epoll file descriptor |
Monitoring file events
| Syscall | Number | Description |
|---|---|---|
| INOTIFY_INIT | 253 | Initialize an inotify instance |
| INOTIFY_INIT1 | 294 | Initialize an inotify instance |
| INOTIFY_ADD_WATCH | 254 | Add a watch to an initialized inotify instance |
| INOTIFY_RM_WATCH | 255 | Remove an existing watch from an inotify instance |
| FANOTIFY_INIT | 300 | Create and initialize fanotify group |
| FANOTIFY_MARK | 301 | Add, remove, or modify an fanotify mark on a filesystem object |
Miscellaneous
| Syscall | Number | Description |
|---|---|---|
| FADVISE64 | 221 | Predeclare an access pattern for file data |
| READAHEAD | 187 | Perform file readahead into page cache |
| GETRANDOM | 318 | Obtain a series of random bytes |