Tag: #system-calls

The magic shell string 3>&2 2>&1 1>&3- swaps stdout and stderr. It does with the dup2 system call to swap file descriptors. 2018-02-22

The domain and type arguments to socket() describe the protocol family and socket type, respectively. The protocol argument specifies the actual protocol to use, which may be inferred from the domain and type. 2017-02-27

A TCP server that uses the fork system call to create a new child process for each accepted connection, allowing it to handle multiple clients concurrently. 2017-02-25

ssize_t is a signed version of size_t, used to represent return values from system calls that may need to indicate error with -1. 2017-02-22

A FIFO is a special file that allows inter-process communication. The mkfifo system call creates a FIFO, enabling processes to read from and write to it. 2017-02-21

A “Hello, world!” program in x86-64 assembly for macOS, using the NASM assembler and system calls for writing to stdout and exiting. 2017-02-20

lsof lists open system resources, including pipes, sockets, and yes, files. It shows their type, owner, and location. 2017-02-20

To close a file descriptor in C, use the close system call. Multiple descriptors can reference the same underlying file or pipe. The pipe is only closed when all references are closed. 2017-02-16

Use the dup system call to duplicate a file descriptor in C, allowing two references to the same underlying pipe. 2017-02-15

To call a program from C, use `fork` then `execve`. There is no more direct way! 2017-02-07

fork duplicates the current process. It returns 0 in the child process. In the parent process, it returns the child’s new process id. 2017-02-06

execve replaces the current process with a new one. It takes a path, an argument array, and an environment array. The process never returns unless execve fails. 2017-02-05

All system calls on macOS 10.12, categorized by the functionality they provide, such as process management, file operations, memory management, etc. 2017-01-31

To write to a file, open the file, mmap the file descriptor, then write to memory. 2017-01-28

mmap is a system call in C that allows programs to manipulate underlying hardware resources, such as physical memory or files, using ordinary memory manipulation. 2017-01-26

Use the times() system call in C to measure the CPU time used by a process, distinguishing between time charged to the process itself and time charged to the kernel on its behalf. 2016-12-26

perror in C prints a human-readable description of the last error that occurred, as stored in the global errno variable. 2016-12-24

The syscalls needed for a simple UDP echo server are socket, bind, recvfrom, sendto, and close. 2016-12-19

Kqueue is a more efficient alternative to select for managing multiple TCP connections, providing a publish-subscribe model for tracking events in the kernel. 2016-12-18

The select syscall allows a process to sleep and wake up when a file descriptor is ready for reading, writing, or has an exceptional condition. This enables a TCP server to handle multiple clients concurrently. 2016-12-16

A minimal TCP server in C uses the socket, bind, listen, accept, recv, send, and close syscalls to manage connections. 2016-12-14