Questions concerning the details of how a program uses system calls to interact with the kernel API, what calls are available, how they work etc.

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How do I get linux-gate.dso on a newer linux system?

I would like to find out which method my 32bit QEMU guest is using for system calls. There's an excellent article explaining linux-gate.dso (http://www.trilithium.com/johan/2005/08/linux-gate/). ...
1
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1answer
438 views

Why system call hooking produces different result everytime in Linux/Android 2.6.29?

I have implemented system call hooking for Android 2.6.29 kernel through a LKM module. I am tracing down one Android app for system calls. But interestingly, it returns different results every time I ...
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2answers
47 views

Is system call the only way that a user program can intentionally affect the state of a Linux kernel?

I think there are several ways that a user program can intentionally affect the state of a Linux kernel. By invoking a system call; By invoking mmap() and writing the memory that has been mapped to ...
6
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1answer
147 views

Some basic questions about Linux kernel's security [closed]

I don't know much about Linux kernel, and I have some questions. What is the main purpose of separating kernel memory from user-space memory? To make sure that a user application cannot do anything ...
1
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1answer
27 views

open() return new file descriptor posix [closed]

I have to set the return values for open() in posix. How do I return "the new file descriptor" as it is said in the Linux man pages: RETURN VALUE open(), openat(), and creat() return the new ...
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4answers
5k views

Difference between system calls and library functions

I have been through the answer of this question but do not quite understand the difference between system calls and library functions. Conceptually, what is the difference between the two?
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3answers
158 views

System calls supported in running Kernel

Is there a way to get the number of or list of system calls supported by currently running Linux Kernel? So I want to find a way to 'read' the syscall table of a running kernel.
1
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1answer
85 views

Strace Hello World program

So I am trying to understand systemcalls with the following "Hello World!" program: #include <stdio.h> int main(){ printf("Hello World!\n"); return 0; } and then I run strace on the ...
2
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1answer
37 views

How to log all the system calls made by a program, say chrome, using linux auditing?

autrace can log the system calls made by a program by running it. I want to log the system calls of already running programs. It can be done by finding the process id, but is there any other elegant ...
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1answer
53 views

List the system calls used in an application

Is there any way to get a list of all system calls used in an application without running through all possible scenarios in the app?
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1answer
21 views

Table or list of system call failure modes?

I am wondering if there is a table or list of system call failure modes. A few examples: Can exit() fail due to the system being out of memory? Can open() fail due to the system reaching the max open ...
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0answers
44 views

Are system calls available in a chroot environment?

I'm experiencing a lot of compilation errors regarding missing system calls (e.g. error: '__NR_name_to_handle_at' undeclared (first use in this function)) with different projects (ganesha 2.1.0 ...
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2answers
3k views

Where is the fork() on the fork bomb :(){ :|: & };:?

Warning: Running this command in most shells will result in a broken system that will need a forced shutdown to fix I understand the recursive function :(){ :|: & };: and what it does. But I ...
7
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1answer
162 views

Why are rmdir and unlink two separate system calls?

Here's something that kept me wondering for a while: [15:40:50][/tmp]$ mkdir a [15:40:52][/tmp]$ strace rmdir a execve("/usr/bin/rmdir", ["rmdir", "a"], [/* 78 vars */]) = 0 brk(0) ...
2
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1answer
56 views

Is there a system call to bind a file descriptor directly into another?

A read() & write() loop would probably be as good as what I'm looking for, but nevertheless is anything like that around or is it impossible because of an obstacle I didn't envisage ? I'm curious
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2answers
936 views

Which is more efficient, ls or ls -l?

As I understand, the ls command calls getdents, which returns up to x number of directory entries. Are there any other system calls involved? If I run ls -l, are there any more system calls? I am ...
2
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1answer
152 views

What is the use of “magic arguments” in Linux reboot system call?

As I was reading Linux source code, and more specifically the system calls code, I came across sys_reboot implementation: http://lxr.free-electrons.com/source/kernel/reboot.c#L199. 199 ...
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1answer
66 views

System calls in linux

Generally, systems provide a library or API that sits between normal programs and the operating system. On Unix-like systems, that API is usually part of an implementation of the C library (libc), ...
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2answers
115 views

Low level system call [closed]

C provides library functions such as write(),read().. for system calls.How to make a system call without using any library in linux in C ?
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3answers
310 views

System calls source code

C library provides functions such as write(),read(),open()...that we can use in our C program to make system calls. where can I find source code for these functions?
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0answers
41 views

difference between system-call, vm-call and hypervisor-call [closed]

What is the difference between system-call, vm-call and hypervisor-call in a virtualized environment?
0
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1answer
56 views

Process's father after setpgid(0,0);

I have a process P1 (child of some parent process P0) both in the same process group. P1 somewhere in his code runs: setpgid(0,0); then a new process group is created (where the group leader is P1). ...
9
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2answers
271 views

How a piped shell programs balance their output/input rates? [duplicate]

Possible Duplicate: Bash while loop and reading from pipe I come from web programming background, and find myself interested in one peculiarity of using a local shell. I understand that ...
3
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1answer
69 views

Get device with major number 0 (btrfs subvolume)

When I stat a file on a btrfs subvolume I get a major device number of 0. Is there a reliable way to find the mount point of this device, without knowing in advance it is a btrfs subvolume? e.g. I'd ...
19
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5answers
60k views

How to find application's path from command line?

For example, I have git installed on my system. But I don't remember where I installed it, so which command is fit to find this out?
9
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5answers
1k views

What is meant by “a system call” if not the implementation in the programing language?

I would like to understand the term "system call". I am familiar that system calls are used to get kernel services from a userspace application. The part i need clarification with is the difference ...
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2answers
3k views

Calculating total CPU system usage in C [closed]

I found this answer on StackOverflow for calculating total CPU usage: http://stackoverflow.com/questions/1420426/calculating-cpu-usage-of-a-process-in-linux/4497769#4497769 But how do I calculate ...
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1answer
75 views

Capture information of system-call

I have a QEMU-KVM hypervisor (ubuntu) with several VMs. What I want to do is capture all information of VMs system call to hypervisor (without any intervention to VM whatsoever) in real time within a ...
1
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0answers
115 views

Passing data from kernel space to user space in FreeBSD [closed]

I need some information regarding write requests from all applications on FreeBSD. I put a function inside the file system write call ffs_write() which collects the information into an array of ...
2
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2answers
224 views
1
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1answer
404 views

Too Much System Time

I have observed that when running CESM (a weather modeling application), the top command shows a great deal of time is spent on system calls, about 25% to 60%, and only 40% to 75% is used in user ...
3
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1answer
54 views

Result from kernel returned to what process?

When a process requires actions that require kernel mode, it uses a system call. So, how are the results returned to the process?
2
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3answers
169 views

In what shared library is read()?

I'm a Linux rookie and want to know where the system call read() is. Which shared library is linked when I call read()?
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2answers
101 views

How to notice log file changes with Linux standard tools? [duplicate]

I need something that does not need to be installed. It's on an embedded system with very little space on the HD. I can't instal anything. I need to do it with something that is already included. I ...
3
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3answers
146 views

API with no system calls

The book 'Understanding Linux Kernel' says that 'for something abstract such as math functions, there may be no reason to make system calls'. Can any one please explain how is a system call not ...
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1answer
480 views

Occasional error from bash on AIX: Interrupted system call

I am experiencing problems with process substitution in bash on AIX It happens very rarely, apparently only when the server is loaded. An example error message is: line 9: /tmp//sh-np-7841523: ...
5
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3answers
342 views

How can you change the process name of Wing IDE from python to something more descriptive

In my process list under Ubuntu (using top/System Monitor) one of the largest memory hogs (200+Mb) was python. I searched a bit for one of my programs to be the cause until I realised this was my ...
0
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1answer
152 views

what is a Kernel? [closed]

I'm learning Unix from the Unix Architecture book by Maurice J Bach. So if my question seems too stupid, please do bear with it. I read a few related questions but I would like a more simple ...
9
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2answers
3k views

Interruption of system calls when a signal is caught

From reading the man pages on the read() and write() calls it appears that these calls get interrupted by signals regardless of whether they have to block or not. In particular, assume a process ...
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0answers
79 views

Which Unixes support cross-device filesystem links (in particular for rename)?

Just read the following on the FreeBSD man page for the rename syscall: ... [EXDEV] The link named by to and the file named by from are on different logical devices (file systems). Note that ...
1
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1answer
55 views

What is a channel?

http://www.di.uevora.pt/~lmr/syscalls.html In that reference about system calls, appears a function called dup(). It is said that it duplicates channels. Then my question is, what is a channel?
0
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1answer
52 views

Which System Call provides an interface for sending messages to devices? [closed]

Question is above. I've looked through the man pages, but they are somewhat unclear on the topic. I'm not sure if I'm looking for sendmsg() or msgsend() or if I'm looking for something totally ...
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2answers
2k views

Which file in kernel specifies fork(), vfork()… to use sys_clone() system call

When ltrace is used for tracing the system calls, I could see that fork() uses sys_clone() rather than sys_fork(). But I couldnt find the linux source where it is defined. My program is ...
12
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2answers
1k views

Equivalent of “truss -T” and “truss -U” on Linux?

Is there an equivalent of what the -T and -U option of the truss Solaris utility does on Linux. Those are to specify a system call (-T) or library function (-U) which when called by the traced ...
8
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4answers
2k views

Why should a child of a vfork or fork call _exit() instead of exit()?

From the man page of vfork(): vfork() differs from fork() in that the parent is suspended until the child makes a call to execve(2) or _exit(2). The child shares all memory with its ...
5
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2answers
93 views

Making a process read a different file for the same filename

I have an application that reads a file. Let's call it processname and the file ~/.configuration. When processname runs it always reads ~/.configuration and can't be configured differently. There are ...
3
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3answers
1k views

Command to trace rsh server to check behaviour of particular system call

I am working with rsh. I want to check the whole process from beginning to end. For that I used strace. Os name is CentOS. I am working on single machine, server and client are on same machine. My ...
0
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0answers
346 views

Tracing system call on Ubuntu 12.04

The main task I have to carry out, is to trace the system call of processes in ubuntu 12.04 LTS. Problem is, I am unable to trace them continuously, i.e. as soon as they are added to the system, they ...
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1answer
110 views

System call tracing [closed]

I am working on system call tracing for host based IDS, i need to trace a process as soon as it entered in the system (a new entry in /proc). Is there any interrupt or signal or kernel datastructure ...
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2answers
73 views

Importance of knowing if a standard library function is executing a system call [closed]

Is it actually important for a programmer to know if the standard library function he/she is using is actually executing a system call? If so, why? Intuitively I'm guessing the only importance is in ...