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: Reads and optionally sets adjustment parameters for clock adjustment algorithm used on Linux (RFC 5905). It behaves like adjtimex(), but 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
mseal: Provides memory protection by allow developers to mark specific memory regions immutable, which helps with exploit mitigation
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 to allow reading or writing data
open_by_handle_at: The open_by_handle_at opens a file handle returned by a name_to_handle_at() and returns an open file descriptor.
openat: Similar to open(), but uses dirfd argument and deals differently with path

P

personality: Set or get the personality for a process, a kernel execution domain
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
prctl: Perform operations on a process or thread, such as changing its capabilities, set name of the calling thread, set the secure computing mode (seccomp), and more.
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
seccomp: Perform operations on the secure computing (seccomp) state of a process
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
sigreturn: Allow implementation of signal handlers
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

wait: Suspend the execution of the calling process thread until one of its child processes terminates.
waitpid: Suspend the execution of the calling process thread until one of the specified child processes (by PID) terminates. By using specific options, also other actions like termination can be waited for. The functionality of this system call is similar to wait(), yet with more control over the children and states.
write: Write to file descriptor
writev: Writes buffers to file