Questions tagged [debugging]

is a process of finding and reducing the number of bugs, or defects, in a computer program, thus making it behave as expected

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163
votes
7answers
320k views

how can I make cron run a job right now, for testing/debugging? without changing the schedule!

I have a cron job that is scheduled to run everyday, other than changing the schedule, is there any other way to do a test run of the command right now to see if it works as intended? EDIT: (from ...
150
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8answers
239k views

How to debug a bash script?

I'm having some problems with some scripts in bash, about errors and unexpected behaviors. I would like to investigate the causes of the problems so I can apply fixes. Is there a way I can turn some ...
83
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3answers
110k views

Linux network troubleshooting and debugging

From time to time Linux and Unix users faced with various network problems. Many of these problems are presented here and at some others troubleshooting forums, but they are very concrete and contains ...
53
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8answers
67k views

Can we get compiler information from an elf binary?

Is there some chance to know how a binary was built, under Linux? (and or other Unix) Compiler, version, time, flags etc... I looked at readelf and couldn't find much, but there might be other ways ...
53
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4answers
3k views

How did `git pull` eat my homework?

I feel like a kid in the principal's office explaining that the dog ate my homework the night before it was due, but I'm staring some crazy data loss bug in the face and I can't figure out how it ...
49
votes
3answers
83k views

How to step-into, step-over and step-out with GDB?

I typed help while I was in the GDB but didn't find anything about step-into, step-over and step-out. I put a breakpoint in an Assembly program in _start (break _start). Afterwards I typed next and it ...
47
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4answers
107k views

How to know where a program is stuck in linux?

I am running the following command on my ubuntu server root@slot13:~# lxc-stop --name pavan --logfile=test1.txt --logpriority=trace It seems to hang indefinitely. Whenever this happened on AIX, I ...
43
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2answers
146k views

Running application ends with “Segmentation Fault”

I have a command line application that when run does not do what it is supposed to do and at a certain point leaves the message: Segmentation fault What does this mean? What should I do?
30
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3answers
6k views

How can I see the exact command line being executed inside some bash instance?

I have a long running bash instance (inside a screen session) that is executing a complex set of commands inside a loop (with each loop doing pipes, redirects, etc). The long command line was ...
27
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5answers
112k views

How to view core files for debugging purposes in Linux?

I want to view the contents of a core file while debugging a program. How can I view the contents of a core file?
22
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4answers
4k views

Kernel Hacking Environment

I have been working in embedded OS like uCOS, ThreadX. While I have coded apps in Linux, now I’m planning to start learning Linux Kernel. I have few questions regarding the environment. Which is best ...
20
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3answers
2k views

How can I see what command was actually run in the shell, through an alias or function

I have a bash function (or alias), for instance function install() {sudo apt-get install $@}. When running the command install dicelab, what I expect will actually be run is sudo apt-get install ...
19
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2answers
20k views

Tools for Debugging Routing Tables on a Linux Machine?

Is there a tool that debugs routing tables on a Linux machine? I mean one that I can use by inputting an ip address into it, it'll take the existing routing table into account and output the ...
19
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2answers
4k views

How to find out what process is writing to STDOUT?

I have two instances of a process running. One of them is "frEAkIng oUT!" and printing errors non stop to STDOUT. I want to kill the broken process but I have to make sure I don't terminate the wrong ...
18
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3answers
33k views

How to compile without optimizations -O0 using CMake

I am using Scientific Linux (SL). I am trying to compile a project that uses a bunch of C++ (.cpp) files. In the directory user/project/Build, I enter make to compile and link all the .cpp files. I ...
17
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1answer
7k views

Debugging scripts, what is the difference between -x to set -euxo pipefail?

The main way I know to debug scripts is adding -x to the shabang (#!/bin/bash -x). I recently came across a new way, adding set -euxo pipefail right under the shabang, as in: #!/bin/bash set -euxo ...
16
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2answers
17k views

Can gdb debug suid root programs?

I wrote a program that calls setuid(0) and execve("/bin/bash",NULL,NULL). Then I did chown root:root a.out && chmod +s a.out When I execute ./a.out I get a root shell. However when I do gdb ...
15
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4answers
4k views

How can I debug a Suspend-to-RAM issue on Linux?

I'm hoping to get experience-based suggestions on how to go about debugging suspend-to-RAM issue. Advice specific to my situation(detailed below) would be great, but I am also interested in general ...
14
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2answers
7k views

strace for library calls

I know of strace, which is super handy for watching system calls. Is there an equivalent that can trace calls to external libraries? For example, I'm trying to debug some SSLeay misbehavior with a ...
14
votes
1answer
4k views

How to make gdb not ask me “y or n”?

When I use GDB command add-symbol-file to load the symbol, GDB always asks me 'y or n', like this: gdb> add-symbol-file mydrv.ko 0xa0070000 add symbol table from file "mydrv.ko" at ....
13
votes
2answers
1k views

Is there a way for shell script to know which program has executed it?

In *nix world, is there a way for shell script to have information about which program has executed it? Example: /path/to/script1 /path/to/script_xyz in this imaginary scenario, script_xyz would ...
13
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3answers
5k views

Is it possible to strace the builtin commands to Bash?

Inspired by this question, titled: When are the built-in commands loaded to memory, while attempting to answer this I tried the following command and was a bit surprised that I couldn't run it: $ ...
13
votes
2answers
16k views

How to passively capture from Unix domain sockets (AF_UNIX socket monitoring)?

TCP/IP and UDP captures can be made using tcpdump/dumpcap and produces a pcap/pcapng file which can be fed to Wireshark for further analysis. Does a similar tool exist for named Unix domain sockets? (...
13
votes
2answers
3k views

Observing a hard-disk write in kernel space (with drivers/modules)

Apologies in advance if this post is a bit dense/messy, but I'm having a hard time formulating it better... Basically, I would like to study what happens upon a hard disk write, and I'd like to know: ...
12
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3answers
40k views

How can we trace problems of crashing programs in Linux?

If an application crashes in Windows we can check the Event Viewer in the Administration tools to see what has crashed. Sometimes it has useful information others not, but it is a start. In linux if ...
12
votes
2answers
8k views

Dump process core without killing the process

Is there a way to get a core dump (or something similar) for a process without actually killing the processes? I have a multithreaded python process running on an embedded system. And I want to be ...
12
votes
2answers
6k 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 ...
11
votes
3answers
45k views

ldd does not find path, How to add

I know this question isn't very new but it seems as if I didn't be able to fix my problem on myself. ldd generate the following output u123@PC-Ubuntu:~$ ldd /home/u123/Programme/TestPr/Debug/TestPr ...
11
votes
3answers
4k views

bash: escape individual lines from `-x` echoing

In bash, when running with the -x option, is it possible to exempt individual commands from echoing? I'm trying to make the output as neat as possible, so I am running certain parts of my script in a ...
11
votes
4answers
1k views

How can I tell if the currently executing bash script has been invoked with -x for debugging?

I have a script launch.sh that executes itself as another user so as to create files with the correct owner. I want to pass -x to this invocation if it was originally passed to the script if [ `...
11
votes
2answers
18k views

Where is vagrant's log file?

I am trying to debug a vagrant- or VirtualBox related problem (see taiga-vagrant fails to provide a working taiga environment #21). The command VAGRANT_LOG=debug vagrant up --debug prints out plenty ...
11
votes
1answer
18k views

ACPI BIOS Error / AE_NOT_FOUND

I'm getting these error messages every single time I reboot my desktop (and a couple of more I don't know how to retain when it's shutting down, but those are not relevant to this question so far): [...
10
votes
4answers
16k views

How to debug a suspend problem?

I used to have Fedora 14 installed on this HP Compaq 610, and the suspend feature worked fine. Now that I've installed Scientific Linux 6.1 suspend doesn't work anymore. How do I debug/fix it?
10
votes
2answers
4k views

How exactly does printk work internally?

I know printf needs help from the OS to do its job. I also know printf does not work in the Linux source code as there is no library. And so we have printk for debugging. How does printk work ...
10
votes
1answer
2k views

Any way to have a “verbose mode” or “debug mode” with sed?

Is there a way to make gnu sed be verbose about what is run and what is done ? I'd like to have something like a "debug mode" so that I can see - for each line of input - the content of the hold space ...
9
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5answers
6k views

How to track/fix a memory-related issue in a large C/C++ code on *nix systems

What strategy you use while tracking a memory-related issue? What tools do you use (open source as well as proprietary) to identify memory leaks, memory corruption etc? How would you track memory ...
9
votes
2answers
6k views

How do I debug a kernel module in which a NULL pointer appears?

I have a custom kernel module that I compiled from this patch that adds support for the logitech G19 keyboard among other G series devices. I compiled it just fine against Ubuntu's maverick kernel's ...
9
votes
1answer
12k views

Where to get “/etc/ld.so.nohwcap” file from? [duplicate]

When I run a command through strace utility I can see access errors such as access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) Now I've read somewhere that what's ...
9
votes
2answers
14k views

How to dump USB traffic?

I got an USB gamepad and I would like to see and inspect the signals and commands that this peripherals is actually sending to my PC/kernel: how I can do that ? I was assuming that something like ...
9
votes
4answers
4k views

Debugging Linux machine freezes

I have 15 identical Linux RH 4.7 64-bit severs. They run cluster database (cluster is application level). On occasion (every month or so) a random box (never the same though) freezes. I can ping the ...
9
votes
1answer
3k views

How to debug system freeze?

I'm experiencing strange bug when I close lid of my laptop - system freezes (no reaction on keys, no response form ssh) hard and displays some strange colour effects. The kernel log (after reboot) ...
9
votes
2answers
9k views

How to enable crash reports/core dumps/stack trace logging globally?

Crashing bugs can be the most annoying ones, leading to data loss, downtime and frustrated users. It would be good if applications crashed less. Because of the complexity of the machine context, ...
8
votes
2answers
831 views

function's calling context in zsh: equivalent of bash `caller`

In bash, I can write: caller 0 and receive the caller context's: Line number Function Script name This is extremely useful for debugging. Given: yelp () { caller 0; } I can then write yelp to ...
8
votes
2answers
2k views

How to determine what instructions a process is executing?

I know about strace and ltrace, but that only tells me what system calls and library calls a process is executing, respectively. I would like to know exactly what instructions a process is executing. ...
8
votes
3answers
4k views

Best practise to diagnose problems [closed]

As Linux/Unix users, we run into problems frequently. And after long hours of problem solving, we develop the skill of debugging. Now, what are good principles, methods or best practises when trying ...
8
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2answers
2k views

Debugging lock-up - systemd loses my logs

Ever since I have "upgraded" to systemd on Arch Linux, I keep losing logs when an unexpected lockup happens. I hit the same log-losing issue one month ago and just hit the issue again. There are also ...
8
votes
1answer
902 views

Tool to trace library calls in Linux/ARM

I am searching for a tool that allows to trace calls to functions in shared libraries in Linux/ARM. Basically, I want to be able to specify a command line and let this tool produce a record of called ...
7
votes
4answers
8k views

Easiest way to find missing quote in a bash a script?

I have a bash script which is currently 700+ lines long. After a particularly long round of editing, it now errors like so: ./run_me.sh: line 693: unexpected EOF while looking for matching `'' ./...
7
votes
2answers
503 views

How to know the code flow of a driver module?

I am studying Linux device drivers, my main focus is on wifi drivers. I want to know how the code flows when I plugin my device. Maybe, I can do something like add a printk line in every function. ...
7
votes
3answers
1k views

Adding comments using 'set -x'

Sometimes it is really handy to just add set -x to the top of your script to show all commands before they are executed. There is only one drawback creating scripts with a decent output: I don't ...

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