If you haven't seen it yet there is a new troubleshooting tool out called
sysdig. It's been touted as
tcpdump and well, it seems like it is living up to the hype. I would actually rather compare
sysdig to SystemTap meets
tcpdump, as it has the command line syntax of
tcpdump but the power of SystemTap.
In this article I am going to cover some basic and cool examples for
sysdig, for a more complete list you can look over the sysdig wiki. However, it seems that even the
sysdig official documentation is only scratching the surface of what can be done with
In this article we will be installing
sysdig on Ubuntu using
apt-get. If you are running an
rpm based distribution you can find details on installing via
Setting up the apt repository
sysdig via apt we will need to setup the apt repository maintained by Draios the company behind
sysdig. We can do this by running the following
# curl -s https://s3.amazonaws.com/download.draios.com/DRAIOS-GPG-KEY.public | apt-key add - # curl -s -o /etc/apt/sources.list.d/draios.list http://download.draios.com/stable/deb/draios.list
The first command above will download the Draios gpg key and add it to apt's key repository. The second will download an apt sources file from Draios and place it into the
Update apt's indexes
Once the sources list and gpg key are installed we will need to re-sync apt's package indexes, this can be done by running
# apt-get update
Kernel headers package
sysdig utility requires the kernel headers package, before installing we will need to validate that the kernel headers package is installed.
Check if kernel headers is installed
The system that I am using for this example already had the kernel headers packaged installed, to validate if they are installed on your system you can use the
# dpkg --list | grep header ii linux-generic 220.127.116.11.13 amd64 Complete Generic Linux kernel and headers ii linux-headers-3.11.0-12 3.11.0-12.19 all Header files related to Linux kernel version 3.11.0 ii linux-headers-3.11.0-12-generic 3.11.0-12.19 amd64 Linux kernel headers for version 3.11.0 on 64 bit x86 SMP ii linux-headers-generic 18.104.22.168.13 amd64 Generic Linux kernel headers
It is important to note that the kernel headers package must be for the specific kernel version your system is running. In the output above you can see the
linux-generic package is version 22.214.171.124 and the headers package is for 126.96.36.199. If you have multiple kernels installed you can validate which version your system is running with the
# uname -r 3.11.0-12-generic
Installing the kernel headers package
To install the headers package for this specific kernel you can use
apt-get. Keep in mind, you must specify the kernel version listed from
# apt-get install linux-headers-<kernel version>
# apt-get install linux-headers-3.11.0-12-generic
Now that the apt repository is setup and we have the required dependencies, we can install the
# apt-get install sysdig
The syntax for
sysdig is similar to
tcpdump in particular the saving and reading of trace files. All of
sysdig's output can be saved to a file and read later just like
tcpdump. This is useful if you are running a process or experiencing an issue and wanted to dig through the information later.
Writing trace files
To write a file we can use the
-w flag with sysdig and specify the file name.
# sysdig -w <output file>
# sysdig -w tracefile.dump
sysdig command can be stopped with
Reading trace files
Once you have written the trace file you will need to use
sysdig to read the file, this can be accomplished with the
# sysdig -r <output file>
# sysdig -r tracefile.dump 1 23:44:57.964150879 0 <NA> (7) > switch next=6200(sysdig) 2 23:44:57.966700100 0 rsyslogd (358) < read res=414 data=<6>[ 3785.473354] sysdig_probe: starting capture.<6>[ 3785.473523] sysdig_probe: 3 23:44:57.966707800 0 rsyslogd (358) > gettimeofday 4 23:44:57.966708216 0 rsyslogd (358) < gettimeofday 5 23:44:57.966717424 0 rsyslogd (358) > futex addr=13892708 op=133(FUTEX_PRIVATE_FLAG|FUTEX_WAKE_OP) val=1 6 23:44:57.966721656 0 rsyslogd (358) < futex res=1 7 23:44:57.966724081 0 rsyslogd (358) > gettimeofday 8 23:44:57.966724305 0 rsyslogd (358) < gettimeofday 9 23:44:57.966726254 0 rsyslogd (358) > gettimeofday 10 23:44:57.966726456 0 rsyslogd (358) < gettimeofday
Output in ASCII
sysdig saves the files in binary, however you can use the
-A flag to have
sysdig output in ASCII.
# sysdig -A
# sysdig -A > /var/tmp/out.txt # cat /var/tmp/out.txt 1 22:26:15.076829633 0 <NA> (7) > switch next=11920(sysdig)
The above example will redirect the output to a file in plain text, this can be helpful if you wanted to save and review the data on a system that doesn't have
sysdig command has filters that allow you to filter the output to specific information. You can find a list of available filters by running
sysdig with the
# sysdig -l ---------------------- Field Class: fd fd.num the unique number identifying the file descriptor. fd.type type of FD. Can be 'file', 'ipv4', 'ipv6', 'unix', 'pipe', 'e vent', 'signalfd', 'eventpoll', 'inotify' or 'signalfd'. fd.typechar type of FD as a single character. Can be 'f' for file, 4 for IPv4 socket, 6 for IPv6 socket, 'u' for unix socket, p for pi pe, 'e' for eventfd, 's' for signalfd, 'l' for eventpoll, 'i' for inotify, 'o' for uknown. fd.name FD full name. If the fd is a file, this field contains the fu ll path. If the FD is a socket, this field contain the connec tion tuple. <truncated output>
Capturing a specific process
You can use the "proc.name" filter to capture all of the
sysdig events for a specific process. In the example below I am filtering on any process named sshd.
# sysdig -r tracefile.dump proc.name=sshd 530 23:45:02.804469114 0 sshd (917) < select res=1 531 23:45:02.804476093 0 sshd (917) > rt_sigprocmask 532 23:45:02.804478942 0 sshd (917) < rt_sigprocmask 533 23:45:02.804479542 0 sshd (917) > rt_sigprocmask 534 23:45:02.804479767 0 sshd (917) < rt_sigprocmask 535 23:45:02.804487255 0 sshd (917) > read fd=3(<4t>10.0.0.12:55993->188.8.131.52:22) size=16384
Capturing all processes that open a specific file
fd.name filter is used to filter events for a specific file name. This can be useful to see what processes are reading or writing a specific file or socket.
# sysdig fd.name=/dev/log 14 11:13:30.982445884 0 rsyslogd (357) < read res=414 data=<6>[ 582.136312] sysdig_probe: starting capture.<6>[ 582.136472] sysdig_probe:
Capturing all processes that open a specific filesystem
You can also use comparison operators with filters such as contains, =, !=, <=, >=, < and >.
# sysdig fd.name contains /etc 8675 11:16:18.424407754 0 apache2 (1287) < open fd=13(<f>/etc/apache2/.htpasswd) name=/etc/apache2/.htpasswd flags=1(O_RDONLY) mode=0 8678 11:16:18.424422599 0 apache2 (1287) > fstat fd=13(<f>/etc/apache2/.htpasswd) 8679 11:16:18.424423601 0 apache2 (1287) < fstat res=0 8680 11:16:18.424427497 0 apache2 (1287) > read fd=13(<f>/etc/apache2/.htpasswd) size=4096 8683 11:16:18.424606422 0 apache2 (1287) < read res=44 data=admin:$apr1$OXXed8Rc$rbXNhN/VqLCP.ojKu1aUN1. 8684 11:16:18.424623679 0 apache2 (1287) > close fd=13(<f>/etc/apache2/.htpasswd) 8685 11:16:18.424625424 0 apache2 (1287) < close res=0 9702 11:16:21.285934861 0 apache2 (1287) < open fd=13(<f>/etc/apache2/.htpasswd) name=/etc/apache2/.htpasswd flags=1(O_RDONLY) mode=0 9703 11:16:21.285936317 0 apache2 (1287) > fstat fd=13(<f>/etc/apache2/.htpasswd) 9704 11:16:21.285937024 0 apache2 (1287) < fstat res=0
As you can see from the above examples filters can be used for both reading from a file or the live event stream.
Earlier I compared
sysdig to SystemTap, Chisels is why I made that reference. Similar tools like SystemTap have a SystemTap only scripting language that allows you to extend the functionality of SystemTap. In
sysdig these are called chisels and they can be written in LUA which is a common programming language. I personally think the choice to use LUA was a good one, as it makes extending
sysdig easy for newcomers.
List available chisels
To list the available chisels you can use the
-cl flag with
# sysdig -cl Category: CPU Usage ------------------- topprocs_cpu Top processes by CPU usage Category: I/O ------------- echo_fds Print the data read and written by processes. fdbytes_by I/O bytes, aggregated by an arbitrary filter field fdcount_by FD count, aggregated by an arbitrary filter field iobytes Sum of I/O bytes on any type of FD iobytes_file Sum of file I/O bytes stderr Print stderr of processes stdin Print stdin of processes stdout Print stdout of processes <truncated output>
The list is fairly long even though
sysdig is still pretty new, and since
sysdig is on GitHub you can easily contribute and extend
sysdig with your own chisels.
Display chisel information
While the list command gives a small description of the chisels you can display more information using the
-i flag with the chisel name.
# sysdig -i bottlenecks Category: Performance --------------------- bottlenecks Slowest system calls Use the -i flag to get detailed information about a specific chisel Lists the 10 system calls that took the longest to return dur ing the capture interval. Args: (None)
Running a chisel
To run a chisel you can run
sysdig with the
-c flag and specify the chisel name.
# sysdig -c topprocs_net Bytes Process ------------------------------ 296B sshd
Running a chisel with filters
Even with chisels you can still use filters to run chisels against specific events.
Capturing all network traffic from a specific process
The below example shows using the
echo_fds chisel against the processes named apache2.
# sysdig -A -c echo_fds proc.name=apache2 ------ Read 444B from 127.0.0.1:57793->184.108.40.206:80 GET /wp-admin/install.php HTTP/1.1 Host: 220.127.116.11 Connection: keep-alive Cache-Control: max-age=0 Authorization: Basic YWRtaW46ZUNCM3lyZmRRcg== Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.152 Safari/537.36 Accept-Encoding: gzip,deflate,sdch Accept-Language: en-US,en;q=0.8
Capturing network traffic exchanged between a specific ip
We can also use the the
echo_fds chisel to show all network traffic for a single ip using the
# sysdig -A -c echo_fds fd.cip=127.0.0.1 ------ Write 1.92KB to 127.0.0.1:58896->18.104.22.168:80 HTTP/1.1 200 OK Date: Thu, 17 Apr 2014 03:11:33 GMT Server: Apache X-Powered-By: PHP/5.5.3-1ubuntu2.3 Vary: Accept-Encoding Content-Encoding: gzip Content-Length: 1698 Keep-Alive: timeout=5, max=100 Connection: Keep-Alive Content-Type: text/html; charset=utf-8
Identify, capture and resolve common issues faced by Red Hat Enterprise Linux administrators using best practices and advanced troubleshooting techniques
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