Tagged Questions

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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1answer
20 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 ...
2
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0answers
31 views

Where is located syscall_table in kernel x86_64? [migrated]

I'm trying to add new System Call to Linux Kernel(x86_64). Based on this article which explained how to add System Call to Kernel(x86). The article says I need to define my System Call name in a file ...
3
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3answers
108 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
74 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
31 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 ...
0
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1answer
50 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
18 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 ...
0
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0answers
42 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 ...
7
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1answer
139 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
votes
1answer
52 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
7
votes
2answers
918 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
votes
1answer
122 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 ...
2
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2answers
96 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
219 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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1answer
64 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), ...
1
vote
0answers
39 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
votes
1answer
48 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). ...
3
votes
1answer
63 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 ...
1
vote
1answer
68 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
114 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 ...
9
votes
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 ...
2
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2answers
219 views

Are system calls the only way to interact with the Linux kernel from user land?

Are there any other interfaces, e.g. the /proc filesystem?
1
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1answer
359 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
52 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
163 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
94 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
votes
3answers
145 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 ...
0
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1answer
427 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: ...
0
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1answer
151 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 ...
1
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0answers
75 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
vote
1answer
54 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
votes
1answer
51 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 ...
21
votes
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 ...
3
votes
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 ...
5
votes
2answers
92 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 ...
12
votes
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 ...
0
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0answers
321 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 ...
-1
votes
1answer
108 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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votes
2answers
72 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 ...
0
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1answer
226 views

Understanding a XINU system call - getstk.c [closed]

I am having trouble conceptually understanding what is going on towards the end of this system call, and why. I understand the getstk.c method returns the highest memory address of available space, ...
5
votes
3answers
322 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 ...
3
votes
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 ...
1
vote
1answer
430 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 ...
2
votes
1answer
514 views

How to decode cmd = 3222823425 in ioctl in Linux 2.6.29

I am just confused like how can I break cmd=3222823425 value into different parts to figure out what this command means actually in the Linux kernel. I know, some functions are making ioctl command ...
2
votes
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 ...
3
votes
1answer
979 views

Program stall under user but runs under root

I am running R job under a normal user john and root. Interestingly, the program stalls under john user but runs quickly under root. Using strace, I found that when john runs the R, the process stalls ...
5
votes
4answers
4k 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?
1
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1answer
85 views

What means the “integer argument” in system call descriptions? [duplicate]

Possible Duplicate: What do the numbers in a man page mean? All system calls described in manpages have an associated number such as exec(3). What is the meaning of this number?
2
votes
2answers
1k views

exec() and system() system calls

I do understand that while exec() does not return after it executes in Unix ,system() may or may not return depending on the situation.But can anyone explain why exec() system call does not return and ...
9
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2answers
265 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 ...