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There are in fact three gradations in system calls. Some system calls return immediately. “Immediately” means that the only thing they need is a little processor time. There's no hard limit to how long they can take (except in real-time systems), but these calls return as soon as they've been scheduled for long enough. These calls are usually called non-...


8

There is no such system call, or set of system calls. It's all done by convention. Back in the old days, when a "terminal" was a large clunky piece of equiment linked to a computer via a cable, "smart terminals" would do things like move the cursor, or draw a line, or fill in a polygon with colors. The smart terminal usually did this via "escape sequenes". ...


8

$ man 2 read ... READ(2) Linux Programmer's Manual READ(2) NAME read - read from a file descriptor SYNOPSIS #include <unistd.h> ...


7

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5

He's saying it's bound by a 64-bit type, which has a maximum value of (2 ^ 64) - 1 unsigned, or (2 ^ 63) - 1 signed (1 bit holds the sign, +/-). The type is not FILE; it's what the implementation uses to track the offset into the file, namely off_t, which is a typedef for a signed 64-bit type.1 (2 ^ 63) - 1 = 9223372036854775807. If a terabyte is 1000 ^ ...


5

Ambition or a overly severe urge for purity can lead you to do in-line assembly. For example, on x86_64 systems, you can do an open(2) system call like this: #include <sys/syscall.h> int linux_open(const char *pathname, unsigned long flags, unsigned long mode) { long ret; asm volatile ("syscall" : "=a" (ret) : "a" (__NR_open), "D"...


5

There are various tools to do this (of which, other than daemontools and perp, I don't have much experience with): daemontools is more or less the "classic" implementation that spawned most of the other modern implementations supervisord minit s6 runit The one we have come to like at my workplace is perp, which was the best featured for our infrastructure. ...


5

Consider: two processes can have the same file open for reading & writing at the same time, so some kind of communication is possible between the two. When process A writes to the file, it first populates a buffer inside its own process-specific memory with some data, then calls write which copies that buffer into another buffer owned by the kernel (in ...


4

Checkout tput. It is a wrapper around ANSI Escape sequences that are supported (the amount of support differs a lot) by almost all terminal emulators. tput will only output the sequence if it is supported by the terminal, therefore you don't have to worry about the support. Or at least you don't have to worry about strange characters being printed in the ...


4

If the hpc doesn't contain required libs, you have 2 options: Ask the admins to install the required libs Build a static executable, which contains all the libs. If possible to go with option (2), just compile it on your machine, then upload to the hpc and run as is. I suspect unless you have mpi/pgas as part of your code, that the performance gain would ...


3

In order to do system calls you normally have to execute some functions on the CPU that are not part of the C language specification. The system calls are either written in assembly for the CPU, and linked against, or some CPU specific inline assembly within a C function is used. Within the Linux kernel there are various macros defined to support this, ...


3

Reasonable and prudent, provided there are clear warnings on what file is failing, and why, so the user can fix the permissions issue. bash probably dates from a more trusting (and prank-ridden) day. Note that user files can legitimately be group writable, if the site has a policy of each user going into a group that only that user is in, otherwise not. (...


3

If you're seeking after the end of the file, you have to write at least one byte at that position: write(fd, "", 1); to have the OS fill the hole with zeros. So if you want to create an empty file of a certain size 1000 with lseek, do: lseek(fd, 999, SEEK_SET); //<- err check write(fd, "", 1); //<- err check ftruncate is probably better and it ...


3

Quote from this answer : As of Linux 4.1, fallocate(2) supports the FALLOC_FL_INSERT_RANGE flag, which allows one to insert a hole of a given length in the middle of a file without rewriting the following data. However, it is rather limited: the hole must be inserted at a filesystem block boundary, and the size of the inserted hole must be a ...


2

A slow system call is something like a TCP socket read() - if you don't have O_ASYNC (or whatever) set, it can wait for ever. A fast system call is something like gettimeofday() or getpid(), both of which return information to the process that the kernel has immediately available. Disk reads fall in the category of slow system calls. If a process does a ...


2

I know this is not the exact answer to your question but the curses library is the stuff you need to do some tui dev. If you're a programmer, looking at its source (available in all open-source unix distributions) will show you how it's done.


2

Of course it can. Depending on your specific needs, you should consider several things: will you need any kind of support or will you be able and allowed (in the long run) to take care of the technical things yourself? For anything production grade an "enterprise" distribution with support seems to be a better option. what architecture do you need to run on?...


2

Just some pointers on how to (possibly) talk with the power daemon. Have a look into the Chromium OS sources (no idea on how much this differs from Chrome OS), there you'll find the power_managers sources which might be helpful: README explains what one can find there, among others: powerd (powerd.cc) Upper power manager. Adjusts device status ...


2

In addition to what Chris Down wrote, I would also recommend monit. It can notably check if a port if open (eg 80) and restart the appropriate service (eg httpd) if this port is closed. See this example for sshd : check process sshd with pidfile /var/run/sshd.pid start program "/etc/init.d/sshd start" stop program "/etc/init.d/sshd stop" if failed port 22 ...


2

Before going there, go read the specifications of the telnet protocol (RFC 854, see also the Wikipedia entry for the full list of RFCs involved). Telnet is a very complex protocol, as it was designed to connect between machines of a wild variety of operating systems, down to different character coding. Moreover, it is recommended to never use it, as it is ...


2

Harvard Extension School, offers an online (and real classroom if you live in the greater Boston area) class on Unix & Linux systems programming. CSCI E-28 Unix/Linux Systems Programming by Prof. Bruce Molay. I highly recommend it, but it is not free. Another option is a set of videos and books by Marshall Kirk McCusick (of BSD fame) about the ...


2

The Design of the UNIX Operating System by Maurice J. Bach -classic book describes the internal algorithms and the structures that form the basis of the UNIX ®operating system and their relationship to the programmer interface


2

You might want to start with something a lot simpler to get started in this sort of thing, as it sounds as if you are new to it. Perhaps the old talk / talkd command line program and daemon would be more approachable? Some valuable resources include APUE, or Advanced Programming in the UNIX Environment (Stevens), UNP, or UNIX Network Programming (Also by ...


2

A couple of things need to be clarified here: There is virtually no difference between a program being on the hard storage or in memory. If the kernel doesn't find the file already mapped into memory, mmap happens and from then on, the file is accessed through the memory pages, mapped into the virtual memory of a program. Note that this whole mechanism is ...


2

As mentioned in other answers, Dan Bernstein's daemontools began a whole family of toolsets that share the same raw mechanisms: Adam Sampson's freedt Bruce Guenter's daemontools-encore Laurent Bercot's s6 My nosh Gerrit Pape's runit Wayne Marshall's perp Under pretty much any of them, one writes a run program that runs/is the dæmon, and a service ...


2

Most of the time your language of choice will provide functions (of some sort) that eventually map to the relevant syscalls. In those cases, just use those and call it a day; no need to consider syscall interfaces at all. In fact, I'd argue that unless you're writing a standard library, there should be no need to consider the lower-level details in the first ...


1

There is good deep and detailed description about system call at kernel side in recent lwn article: http://lwn.net/Articles/604287/ .


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If you want source code for standard C library, look at the link @goldilocks provided. If you want source code for linux system call, you must search through the linux source code. System call is defined in many locations of linux source. You can grep for string macro SYSCALL_DEFINE: grep -r -n SYSCALL_DEFINE /path/to/linux_source Some of them you can see ...


1

Puppet allows you to define which services should be running on your system. Puppet is IT automation software that helps system administrators manage infrastructure throughout its lifecycle, from provisioning and configuration to patch management and compliance. Using Puppet, you can easily automate repetitive tasks, quickly deploy critical applications, ...


1

There's also God. God is an easy to configure, easy to extend monitoring framework written in Ruby. Keeping your server processes and tasks running should be a simple part of your deployment process. God aims to be the simplest, most powerful monitoring application available. Write a simple server, simple.rb: loop do puts 'Hello' sleep 1 ...


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