SystemTap: Working With System Monitoring Scripts

This is the third and final part of our SystemTap series. This article assumes that you are familiar with SystemTap basics and that you have installed Docker on your AWS EC2 instance with a minimal Red Hat Enterprise Linux 7 platform container. Now we’ll explore working with actual SystemTap scripts to monitor processes and events.

Locating the sample SystemTap scripts

Writing SystemTap scripts for the first time can be a rather daunting experience, especially if you do not have much development experience. Fortunately, SystemTap comes with a large collection of sample scripts that you can use right out of the box. These scripts are all archived into the systemtap-client RPM package. The package is installed, along with other related RPM packages, when you install the SystemTap package.

$ rpm -q --whatrequires systemtap-client
systemtap-2.6-10.el7_1.x86_64

To find out where the examples are stored, we can list the files in the systemtap-client package.

$ rpm -ql systemtap-client | grep examples | head -5
/usr/share/doc/systemtap-client-2.6/examples
/usr/share/doc/systemtap-client-2.6/examples/README
/usr/share/doc/systemtap-client-2.6/examples/general
/usr/share/doc/systemtap-client-2.6/examples/general/alias_suffixes.meta
/usr/share/doc/systemtap-client-2.6/examples/general/alias_suffixes.stp

Once inside the examples directory, take a quick look at the index.txt file, which contains an index of all the examples, along with a short description of what each does, and instructions.

$ cd /usr/share/doc/systemtap-client-2.6/examples
$ head index.txt
SYSTEMTAP EXAMPLES INDEX
(see also keyword-index.txt)
general/alias_suffixes.stp - Count I/O Syscalls using Alias Suffixes
keywords: io statistics
  alias_suffixes.stp is a demonstration of how alias suffixes in the
  systemtap language might be used. The script tracks the wall clock
  time for each invocation of the system calls open, close, read, and
  write. When the script exists it prints out the minimum, average, and

We will run these examples on our docker service and the container. So the output examples below will make sense to you, remember that “PID 1752” refers to the docker service, and “PID 4847” refers to the docker container.

$ ps aux | grep docker | head -2
$ ps aux | grep docker | head -2
root 1752 0.2 2.2 510948 22644 ? Ssl 04:17 0:01 /usr/bin/docker -d --selinux-enabled --add-registry registry.access.redhat.com
root 1752 0.2 2.2 510948 22644 ? Ssl 04:17 0:01 /usr/bin/docker -d --selinux-enabled --add-registry registry.access.redhat.com
ec2-user 4847 0.0 0.7 136348 7412 pts/0 Sl+ 04:27 0:00 docker run -ti rhel7 /bin/bash

pfiles.stp

The pfiles.stp script was written to produce outputs similar to a well-known Solaris tool. It reports on all open files, selected by the process ID. This tool is useful because it gives you more detail than what you would get by looking at the /proc/PID/fd directory, or by using the netstat command.

pfiles.stp is able to list all the open file descriptors along with permissions, user and group IDs, and flags used with the open(3) function call. We also get information about things like open sockets, the peername, and sock options.

$ stap -g pfiles.stp -x 4847 # docker service
  4847: docker
  Current rlimit: 256 file descriptors
   0: S_IFCHR mode:0620 dev:0,11 ino:3 uid:1000 gid:1000 rdev:136,0
      O_RDWR|O_LARGEFILE
      /dev/pts/0
   1: S_IFCHR mode:0620 dev:0,11 ino:3 uid:1000 gid:1000 rdev:136,0
      O_RDWR|O_LARGEFILE
      /dev/pts/0
   2: S_IFCHR mode:0620 dev:0,11 ino:3 uid:1000 gid:1000 rdev:136,0
      O_RDWR|O_LARGEFILE
      /dev/pts/0
   3: S_IFSOCK mode:0777 dev:0,6 ino:67819 uid:1000 gid:1000 rdev:0,0
      O_RDWR|O_NONBLOCK FD_CLOEXEC
      socket:[67819]
      SO_BROADCAST,SO_TYPE(2),SO_SNDBUF(212992),SO_RCVBUF(212992)
        sockname: AF_UNIX
        peername: AF_UNIX /run/systemd/journal/socket
   4:  mode:0600 dev:0,9 ino:4680 uid:1000 gid:1000 rdev:0,0
      O_RDWR FD_CLOEXEC
      anon_inode:[eventpoll]
   5: S_IFSOCK mode:0777 dev:0,6 ino:67907 uid:1000 gid:1000 rdev:0,0
      O_RDWR|O_NONBLOCK FD_CLOEXEC
      socket:[67907]
      SO_BROADCAST,SO_TYPE(1),SO_SNDBUF(212992),SO_RCVBUF(212992)
        sockname: AF_UNIX
        peername: AF_UNIX /var/run/docker.sock
        peercred pid: 1752
   6: S_IFSOCK mode:0777 dev:0,6 ino:67820 uid:1000 gid:1000 rdev:0,0
      O_RDWR|O_NONBLOCK FD_CLOEXEC
      socket:[67820]
      SO_BROADCAST,SO_TYPE(1),SO_SNDBUF(212992),SO_RCVBUF(212992)
        sockname: AF_UNIX
        peername: AF_UNIX /var/run/docker.sock
        peercred pid: 1752

plimit.stp

The plimit.stp script is another tool inspired by the Solaris world. You can use the script to display the user limits of any running process in the instance. This is useful if you are trying to troubleshoot a process that was not started on the command-line. For example, if a process crashes randomly, and you were unable to capture the coredump of the process, running plimit.stp will tell you the user limits of the process without modifying any files.

$ stap -g plimit.stp -x 4847 # docker container
4847:  -docker
 resource                    current    maximum
coredump(blocks)            0          unlimited
data(bytes)                 unlimited  unlimited
max nice                    0          0
file size(blocks)           unlimited  unlimited
pending signals             3836       3836
max locked memory(bytes)    65536      65536
max memory size(bytes)      unlimited  unlimited
open files                  1024       4096
POSIX message queues(bytes) 819200     819200
max rt priority             0          0
stack size(bytes)           8388608    unlimited
cpu time(seconds)           unlimited  unlimited
max user processes          3836       3836
virtual memory(bytes)       unlimited  unlimited
file locks                  unlimited  unlimited

errsnoop.stp

The errsnoop.stp script prints out a list of failing system calls every five seconds. You can find out what these error strings mean by referring to the errno(3) manpages. This is particularly useful if a process takes a long time to start or has trouble accessing certain resources. Here, it’s interesting to see that our docker service is unable to open /proc/stat:

$ ./errsnoop.stp | grep docker
   5  13/EACCES                 open          docker  1752 "/proc/stat", O_RDONLY|O_CLOEXEC
   5 128/EKEYREVOKED            read          docker  1752 13, 0xc20814f800, 128
   5   1/EPERM                 futex          docker  1752 0x12c4100, FUTEX_WAKE, 1
   5   1/EPERM                 futex          docker  1752 0xc208582b58, FUTEX_WAKE, 1
   1 110/ETIMEDOUT             futex          docker  1752 0x12c3db8, FUTEX_WAIT, 0, [0.999796991]
   1 110/ETIMEDOUT             futex          docker  1752 0x12c3db8, FUTEX_WAIT, 0, [0.999827729]
   1 110/ETIMEDOUT             futex          docker  1752 0x12c3db8, FUTEX_WAIT, 0, [0.999799954]
   1 110/ETIMEDOUT             futex          docker  1752 0x12c3db8, FUTEX_WAIT, 0, [0.999841908]

procmod_watcher.stp

The procmod_watcher.stp script logs whenever a process is created or terminated and whenever a kernel module is loaded or unloaded.

In this example, we ran the script with the command “sudo systemctl restart docker.” Unless you are very familiar with systemctl, it may not be so easy to figure out exactly what systemctl is doing when you restart docker. Fortunately, SystemTap can help:

$ stap procmod_watcher.stp -c "sudo systemctl restart docker" | grep docker
   0.011810: EXEC: (8171) stapio: file "/usr/local/bin/sudo" "systemctl" "restart" "docker"
   0.011819: EXEC: (8171) stapio: file "/usr/bin/sudo" "systemctl" "restart" "docker"
   0.017636: EXEC: (8174) sudo: file "/bin/systemctl" "restart" "docker"
   0.035394: EXIT: (8114) docker: exit code 0
   0.035434: EXIT: (8114) docker: exit code 0
   0.035451: EXIT: (8114) docker: exit code 0
   0.035456: EXIT: (8114) docker: exit code 0
   0.035460: EXIT: (8114) docker: exit code 0
   0.035468: EXIT: (8114) docker: exit code 0
   0.041299: EXEC: (8178) (ge-setup): file "/usr/bin/docker-storage-setup"
   0.045473: EXEC: (8179) docker-storage-: file "/usr/bin/awk" "$2 ~ /^\\/$/ && $1 !~ /rootfs/ { print $1 }" "/proc/mounts"
   0.046951: EXEC: (8181) docker-storage-: file "/usr/sbin/lvs" "--noheadings" "-o" "vg_name" "/dev/xvda2"
   0.049275: EXEC: (8182) docker-storage-: file "/usr/bin/sed" "-e" "s/^ *//" "-e" "s/ *$//"
   0.053543: EXIT: (8180) docker-storage-: exit code 0
   0.054163: EXEC: (8186) docker-storage-: file "/usr/bin/awk" "$2 ~ /^$/ { print $1 }"
   0.054828: EXEC: (8185) docker-storage-: file "/usr/sbin/pvs" "--noheadings" "-o" "pv_name,vg_name"
   0.060271: EXIT: (8184) docker-storage-: exit code 0
   0.060702: EXEC: (8188) docker-storage-: file "/usr/bin/grep" "-e" "^DOCKER_STORAGE_OPTIONS=.*dm\\.datadev" "-e" "^DOCKER_STORAGE_OPTIONS=.*dm\\.metadatadev" "/etc/sysconfig/docker-storage"
   0.062484: EXEC: (8192) docker-storage-: file "/usr/bin/grep" "-e" "^DOCKER_STORAGE_OPTIONS=" "/etc/sysconfig/docker-storage"
   0.063171: EXEC: (8193) docker-storage-: file "/usr/bin/sed" "s/DOCKER_STORAGE_OPTIONS=//"
   0.063873: EXEC: (8194) docker-storage-: file "/usr/bin/sed" "s/^ *//"
   0.064545: EXIT: (8191) docker-storage-: exit code 0
   0.064686: EXIT: (8190) docker-storage-: exit code 0
   0.064822: EXIT: (8189) docker-storage-: exit code 0
   0.065364: EXEC: (8196) docker-storage-: file "/usr/sbin/lvs" "--noheadings" "-o" "lv_name,lv_attr" "--separator" ","
   0.067287: EXEC: (8197) docker-storage-: file "/usr/bin/sed" "-e" "s/^ *//"
   0.069905: EXIT: (8195) docker-storage-: exit code 0
   0.070225: EXEC: (8199) docker-storage-: file "/usr/sbin/lvs" "-a" "/docker-poolmeta" "--noheadings"
   0.074710: EXIT: (8201) docker-storage-: exit code 0
   0.075442: EXEC: (8202) docker-storage-: file "/usr/sbin/vgs" "--noheadings" "--nosuffix" "--units" "b" "-o" "vg_free"
   0.079933: EXEC: (8206) docker-storage-: file "/usr/sbin/vgs" "--noheadings" "--nosuffix" "--units" "b" "-o" "vg_free"
   0.084066: EXIT: (8205) docker-storage-: exit code 0
   0.084248: EXIT: (8204) docker-storage-: exit code 0
   0.084526: EXEC: (8208) docker-storage-: file "/usr/sbin/lvcreate" "-y" "-L" "2G" "-n" "docker-pool"
   0.088921: EXIT: (8178) docker-storage-: exit code 3
   0.092796: EXEC: (8210) (docker): file "/usr/bin/docker" "-d" "--selinux-enabled" "--add-registry" "registry.access.redhat.com"
   0.136584: EXEC: (8232) docker: file "/usr/sbin/blkid" "-s" "UUID" "-o" "value" "/dev/mapper/docker-202:2-51421425-base"
   0.143531: EXEC: (8235) docker: file "/usr/sbin/modprobe" "-va" "bridge" "nf_nat" "br_netfilter"
   0.150252: EXEC: (8237) docker: file "/usr/sbin/iptables" "--wait" "-L" "-n"
   0.152227: EXEC: (8238) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-D" "PREROUTING" "-m" "addrtype" "--dst-type" "LOCAL" "-j" "DOCKER"
   0.153454: EXEC: (8239) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-D" "OUTPUT" "-m" "addrtype" "--dst-type" "LOCAL" "!" "--dst" "127.0.0.0/8" "-j" "DOCKER"
   0.154539: EXEC: (8240) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-D" "OUTPUT" "-m" "addrtype" "--dst-type" "LOCAL" "-j" "DOCKER"
   0.155566: EXEC: (8241) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-D" "PREROUTING"
   0.157902: EXEC: (8242) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-D" "OUTPUT"
   0.158890: EXEC: (8243) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-F" "DOCKER"
   0.159845: EXEC: (8244) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-X" "DOCKER"
   0.161416: EXEC: (8245) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-C" "POSTROUTING" "-s" "172.17.42.1/16" "!" "-o" "docker0" "-j" "MASQUERADE"
   0.162433: EXEC: (8246) docker: file "/usr/sbin/iptables" "--wait" "-D" "FORWARD" "-i" "docker0" "-o" "docker0" "-j" "DROP"
   0.163386: EXEC: (8247) docker: file "/usr/sbin/iptables" "--wait" "-t" "filter" "-C" "FORWARD" "-i" "docker0" "-o" "docker0" "-j" "ACCEPT"
   0.164340: EXEC: (8248) docker: file "/usr/sbin/iptables" "--wait" "-t" "filter" "-C" "FORWARD" "-i" "docker0" "!" "-o" "docker0" "-j" "ACCEPT"
   0.165282: EXEC: (8249) docker: file "/usr/sbin/iptables" "--wait" "-t" "filter" "-C" "FORWARD" "-o" "docker0" "-m" "conntrack" "--ctstate" "RELATED,ESTABLISHED" "-j" "ACCEPT"
   0.166313: EXEC: (8250) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-n" "-L" "DOCKER"
   0.167186: EXEC: (8251) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-N" "DOCKER"
   0.168139: EXEC: (8252) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-C" "PREROUTING" "-m" "addrtype" "--dst-type" "LOCAL" "-j" "DOCKER"
   0.169198: EXEC: (8253) docker: file "/usr/sbin/iptables" "-t" "nat" "-S" "PREROUTING"
   0.170098: EXEC: (8254) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-A" "PREROUTING" "-m" "addrtype" "--dst-type" "LOCAL" "-j" "DOCKER"
   0.171181: EXEC: (8255) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-C" "OUTPUT" "-m" "addrtype" "--dst-type" "LOCAL" "-j" "DOCKER" "!" "--dst" "127.0.0.0/8"
   0.172222: EXEC: (8256) docker: file "/usr/sbin/iptables" "-t" "nat" "-S" "OUTPUT"
   0.173137: EXEC: (8257) docker: file "/usr/sbin/iptables" "--wait" "-t" "nat" "-A" "OUTPUT" "-m" "addrtype" "--dst-type" "LOCAL" "-j" "DOCKER" "!" "--dst" "127.0.0.0/8"
   0.174241: EXEC: (8258) docker: file "/usr/sbin/iptables" "--wait" "-t" "filter" "-n" "-L" "DOCKER"
   0.175224: EXEC: (8259) docker: file "/usr/sbin/iptables" "--wait" "-t" "filter" "-C" "FORWARD" "-o" "docker0" "-j" "DOCKER"
WARNING: Number of errors: 0, skipped probes: 2

I do wonder, however, why we are not using firewall-cmd – since that is the new way to interact with netfilter. Perhaps you might have some insights to share in our comments.

I hope this gives you a sense of just how powerful SystemTap can be. Let this be the beginning of your learning journey.

Avatar

Written by

Eugene Teo

Eugene Teo is a director of security at a US-based technology company. He is interested in applying machine learning techniques to solve problems in the security domain.


Related Posts

Patrick Navarro
Patrick Navarro
— January 22, 2020

Top 5 AWS Salary Report Findings

At the speed the cloud tech space is developing, it can be hard to keep track of everything that’s happening within the AWS ecosystem. Advances in technology prompt smarter functionality and innovative new products, which in turn give rise to new job roles that have a ripple effect on t...

Read more
  • AWS
  • salary
Alisha Reyes
Alisha Reyes
— January 6, 2020

New on Cloud Academy: Red Hat, Agile, OWASP Labs, Amazon SageMaker Lab, Linux Command Line Lab, SQL, Git Labs, Scrum Master, Azure Architects Lab, and Much More

Happy New Year! We hope you're ready to kick your training in overdrive in 2020 because we have a ton of new content for you. Not only do we have a bunch of new courses, hands-on labs, and lab challenges on AWS, Azure, and Google Cloud, but we also have three new courses on Red Hat, th...

Read more
  • agile
  • AWS
  • Azure
  • Google Cloud Platform
  • Linux
  • OWASP
  • programming
  • red hat
  • scrum
Alisha Reyes
Alisha Reyes
— December 24, 2019

Cloud Academy’s Blog Digest: Azure Best Practices, 6 Reasons You Should Get AWS Certified, Google Cloud Certification Prep, and more

Happy Holidays from Cloud Academy We hope you have a wonderful holiday season filled with family, friends, and plenty of food. Here at Cloud Academy, we are thankful for our amazing customer like you.  Since this time of year can be stressful, we’re sharing a few of our latest article...

Read more
  • AWS
  • azure best practices
  • blog digest
  • Cloud Academy
  • Google Cloud
Avatar
Guy Hummel
— December 12, 2019

Google Cloud Platform Certification: Preparation and Prerequisites

Google Cloud Platform (GCP) has evolved from being a niche player to a serious competitor to Amazon Web Services and Microsoft Azure. In 2019, research firm Gartner placed Google in the Leaders quadrant in its Magic Quadrant for Cloud Infrastructure as a Service for the second consecuti...

Read more
  • AWS
  • Azure
  • Google Cloud Platform
Alisha Reyes
Alisha Reyes
— December 10, 2019

New Lab Challenges: Push Your Skills to the Next Level

Build hands-on experience using real accounts on AWS, Azure, Google Cloud Platform, and more Meaningful cloud skills require more than book knowledge. Hands-on experience is required to translate knowledge into real-world results. We see this time and time again in studies about how pe...

Read more
  • AWS
  • Azure
  • Google Cloud
  • hands-on
  • labs
Alisha Reyes
Alisha Reyes
— December 5, 2019

New on Cloud Academy: AWS Solution Architect Lab Challenge, Azure Hands-on Labs, Foundation Certificate in Cyber Security, and Much More

Now that Thanksgiving is over and the craziness of Black Friday has died down, it's now time for the busiest season of the year. Whether you're a last-minute shopper or you already have your shopping done, the holidays bring so much more excitement than any other time of year. Since our...

Read more
  • AWS
  • AWS solution architect
  • AZ-203
  • Azure
  • cyber security
  • FCCS
  • Foundation Certificate in Cyber Security
  • Google Cloud Platform
  • Kubernetes
Avatar
Cloud Academy Team
— December 4, 2019

Understanding Enterprise Cloud Migration

What is enterprise cloud migration? Cloud migration is about moving your data, applications, and even infrastructure from your on-premises computers or infrastructure to a virtual pool of on-demand, shared resources that offer compute, storage, and network services at scale. Why d...

Read more
  • AWS
  • Azure
  • Data Migration
Wendy Dessler
Wendy Dessler
— November 27, 2019

6 Reasons Why You Should Get an AWS Certification This Year

In the past decade, the rise of cloud computing has been undeniable. Businesses of all sizes are moving their infrastructure and applications to the cloud. This is partly because the cloud allows businesses and their employees to access important information from just about anywhere. ...

Read more
  • AWS
  • Certifications
  • certified
Avatar
Andrea Colangelo
— November 26, 2019

AWS Regions and Availability Zones: The Simplest Explanation You Will Ever Find Around

The basics of AWS Regions and Availability Zones We’re going to treat this article as a sort of AWS 101 — it’ll be a quick primer on AWS Regions and Availability Zones that will be useful for understanding the basics of how AWS infrastructure is organized. We’ll define each section,...

Read more
  • AWS
Avatar
Dzenan Dzevlan
— November 20, 2019

Application Load Balancer vs. Classic Load Balancer

What is an Elastic Load Balancer? This post covers basics of what an Elastic Load Balancer is, and two of its examples: Application Load Balancers and Classic Load Balancers. For additional information — including a comparison that explains Network Load Balancers — check out our post o...

Read more
  • ALB
  • Application Load Balancer
  • AWS
  • Elastic Load Balancer
  • ELB
Albert Qian
Albert Qian
— November 13, 2019

Advantages and Disadvantages of Microservices Architecture

What are microservices? Let's start our discussion by setting a foundation of what microservices are. Microservices are a way of breaking large software projects into loosely coupled modules, which communicate with each other through simple Application Programming Interfaces (APIs). ...

Read more
  • AWS
  • Docker
  • Kubernetes
  • Microservices
Nisar Ahmad
Nisar Ahmad
— November 12, 2019

Kubernetes Services: AWS vs. Azure vs. Google Cloud

Kubernetes is a popular open-source container orchestration platform that allows us to deploy and manage multi-container applications at scale. Businesses are rapidly adopting this revolutionary technology to modernize their applications. Cloud service providers — such as Amazon Web Ser...

Read more
  • AWS
  • Azure
  • Google Cloud
  • Kubernetes