Overview of Linux syscalls

A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z

A

accept: Accept a connection on a socket
access: Checks whether the calling process can access the pathname, dereferenced when it is a symbolic link
add_key: Create or update a key for kernel key management facility
adjtimex: Reads and optionally sets adjustment parameters for clock adjustment algorithm used on Linux (RFC 5905)
alarm: Schedule an alarm; it lets the system generate a SIGALRM signal for the process after a specified time

B

bind: Assigns address to a socket that was created with socket()
brk: Change the location of program break, specifically the end of the process's data segment

C

cacheflush: Flushes contents of cache(s) for user addresses in specified range
capget: Retrieve thread capabilities
capset: Set thread capabilities
chdir: Change work directory
chmod: Change mode of the file, dereferenced for symbolic links
chown: Changes ownership of file specified by pathname, dereferenced if file is a symbolic link
clock_adjtime: Behaves like adjtimex(), takes an additional clk_id argument to define the clock
clock_getres: Retrieve the resolution (precision) of a specified clock
clock_gettime: Retrieve time from specified clock
clock_settime: Set time of specified clock
clone: Similar to fork() to create a child process, with more fine-grained options to define what is shared between calling process and child. This system call can also make a new process part of newly created namespace by specifying a flag.
clone2: Specific for ia64 platform, similar to clone() but with different handling of stack assignment
clone3: Provides superset of the functionality of the older clone() interface to create child process
close: Close file descriptor
connect: Initiate connection on a defined socket
creat: Like open(), but sets flags O_CREAT|O_WRONLY|O_TRUNC
create_module: Deprecated syscall to create an entry to load a kernel module and reserve the kernel memory for it

D

delete_module: Tries to remove an unused loadable module entry which is related currently loaded Linux kernel module (LKM)
dup: Duplicate file descriptor; more specifically it allocates a new file descriptor that also refers to open file description oldfd
dup2: Same as dup(), duplicate file descriptor; difference is that it uses file descriptor number specified in newfd
dup3: Same as dup2(); difference is that caller can force close-on-exec flag (O_CLOEXEC) to be set

E

epoll_ctl: Manage (add, modify, remove) entries in epoll instance, which is used to monitor if I/O is allowed on the defined set of file descriptors. Similar to poll(), with additional benefits.
execve: Executes the program referred to by specified pathname
exit: Terminates the calling process, parent process will receive a SIGCHLD signal

F

faccessat: Similar to access(), works slightly different when pathname is relative
faccessat2: Closely similar to faccessat() but implements flags argument to correct incorrect implementation in faccessat()
fchdir: Similar to chdir, but uses open file descriptor
fchmod: Same as chmod, but used file by open file descriptor fd
fchmodat: Similar to chmod(), works slightly different when pathname is relative
fchown: Changes ownership of file, referred to by open file descriptor (fd)
fchownat: Similar to fchown(), but deals differently with relative paths
fcntl: Performs an action on file defined by a file descriptor, such as setting flags
finit_module: Similar to init_module(); loads image (ELF) but refers to a file description
flock: Apply or remove advisory lock on file
fork: Create a new child process by duplicating the calling process, with caller becoming the parent process
fstat: Similar to stat(), but uses file descriptor fd
fstatat: More generic interface to receive information that is similar to stat(), fstat(), and lstat()
fstatfs: Similar to statfs(), but uses open file referenced by descriptor fd.
ftruncate: Truncate a file open for writing to specified number of bytes, which may fill it with null bytes (\0) or decrease its size and losing data
futex: Provides a method for waiting until certain condition becomes true

G

get_current_dir_name: Like getcwd(); will retrieve current working directory but creates an array to store the value
getcwd: Copies the absolute pathname of current working directory to a buffer
getdents: Retrieve entries from a directory
getegid: Returns effective group ID of the calling process
geteuid: Retrieve effective user ID of calling process
getgid: Returns real group ID of the calling process
getgroups: Returns supplementary group IDs of calling process
getpeername: Receive address of the peer connected to a socket
getpgid: Retrieve process group ID (PGID)
getpid: Returns process ID (PID) of calling process
getppid: Returns process ID (PID) of parent of the calling process
getrandom: Receive random bytes
getrlimit: Get resource limits
getsid: Receive session ID of a defined process
getsockname: Retrieve current address of defined socket
getsockopt: Get options for socket
gettid: Returns thread ID (TID) of caller. Same as process ID (PID) for single-threaded applications, otherwise different
gettimeofday: Get time or timezone
getuid: Retrieve real user ID of calling process
getwd: Retrieves current working directory in specified pointer to a related buffer; deprecated for security and portability reasons

I

init_module: Load image (ELF) into the kernel space including the required steps to initialize it, including triggering the init() function of the module
io_cancel: Attempts to cancel asynchronous I/O operation that was submitted by io_submit()
io_submit: Submit asynchronous I/O blocks for processing, can be cancelled with io_cancel()

K

kexec_file_load: Similar to kexec_load(), but uses file descriptor for kernel and initrd (initial ram disk)
kexec_load: Load new kernel for later execution
keyctl: Allow user-space programs to take actions on keys, such as updating, revocation, ownership

L

lchown: Like chown(), does not dereference symbolic links
link: Create new link (hard link) to existing file
linkat: Similar to link(), but deals differently with relative paths
listen: Marks socket as a passive to allow it accepting incoming connections with accept()
lseek: Reposition file offset for read/write
lstat: Similar to stat(), but if pathname is symbolic link, return information about link and not the file that symbolic link points to

M

mkdir: Create directory
mkdirat: Similar to mkdir() but deals differently with relative paths
mknod: Create filesystem node (file, device special file, or named pipe) named pathname
mknodat: Similar to mknod, works slightly different when pathname is relative
mlock: Lock pages in a specified address range, so they are guaranteed to stay in memory instead of being swapped to disk
mlock2: Same as mlock() if flags is 0. With flag MLOCK_ONFAULT is locks the current resident pages, the mark the range so currently nonresident pages are locked later when they are used (page fault)
mlockall: Similar to mlock, but tries to lock all the memory pages of the calling process to prevent swapping
mmap: Create new mapping in the virtual address space of the calling process
munlock: Opposite of mlock() to release lock on memory area, so it can be swapped to disk if needed
munlockall: Unlocks all memory pages of calling process so it can be swapped to disk again by the kernel
munmap: Deletes the mappings for specified address range and marks range to generate invalid memory references

N

nice: Change process priority, with +19 (lowest priority) up to to -20 (high priority)
ntp_adjtime: Doing same task as adjtimex(), but is a more portable interface

O

open: Opens file specified by pathname
openat: Similar to open(), but uses dirfd argument and deals differently with path

P

pipe: Create a pipe that allows unidirectional communication between processes
pipe2: Similar to pipe(), to create a channel between two processes. With flag O_DIRECT it will use packet-style communication instead of a stream
poll: Similar task to select(2), which is waiting for a set of file descriptors to become available for I/O.
ppol: Let an application wait until file descriptor is available or signal is caught
prlimit: Get and sets resource limit, combines getrlimit() and setrlimit()
ptrace: Process tracing; usually for breakpoint debugging and system call tracing

R

read: Read from file descriptor
readdir: Read a directory
readv: Read buffers from file
reboot: Reboots the system, or enables/disables reboot keystroke (default: Ctrl+Alt+Delete; changed using loadkeys(1))
recv: Like read(), but normally only used on a socket and has additional flags that can be set
recvfrom: Receives a message on a socket, close to recv(), but with additional flags related to receiving source
recvmsg: Receives a message on a socket with a predefined structure to minimize the number of arguments
rename: Rename a file, move it between directories if required
renameat: Similar to rename(), with deals differently with relative paths
renameat2: Similar to renameat() when no flags are provided, otherwise it has additional options
request_key: Request a key from kernel key management facility
rmdir: Delete directory

S

sbrk: Change the location of program break, specifically it increments the program's data space
select: Let a program monitor multiple file descriptors until one or more become available for I/O actions. This system call has limitations and typically poll or epoll is used.
sendfile: Copies data between one file descriptor and another
setgid: Set effective group ID of calling process, with CAP_SETGID capability it also sets real GID and saved set-group-ID
setgroups: Defines supplementary group IDs of calling process
setpgid: Set process group ID (PGID)
setrlimit: Set resource limits
setsockopt: Set options on socket
settimeofday: Set time or timezone
setuid: Set effective user ID of calling process, with CAP_SETUID capability it also sets real UID and saved set-user-ID
socket: Create endpoint for communication and return file descriptor
socketpair: Create a pair of connected sockets, for example for communication between parent and child process
stat: Get information about file
statfs: Returns information about mounted file system
symlink: Create symbolic link
symlinkat: Similar to symlink() but deals differently with relative paths

T

tee: Duplicate pipe content, does not consume the data
time: Return time; as number of seconds since the Epoch (1970-01-01 00:00:00 +0000 (UTC))
times: Get process and child process times, including CPU time in userspace and by the system for the calling process, and similar for the child processes
truncate: Truncate a writable file to specified number of bytes, which may fill it with null bytes (\0) or decrease its size and losing data

U

umask: Set file mode creation mask
uname: Retrieve name and information about the current kernel
unlink: Delete name from filesystem
unlinkat: Similar to unlink() but deals differently with relative paths
utime: Change access and modification times of inode
utimes: Similar to utime(), but uses array instead of a structure

W

write: Write to file descriptor
writev: Writes buffers to file