Weight: 6
Description: Candidates should be able to measure hardware resource and network bandwidth, identify and troubleshoot resource problems.
Key Knowledge Areas:
- Measure CPU usage
- Measure memory usage
- Measure disk I/O
- Measure network I/O
- Measure firewalling and routing throughput
- Map client bandwidth usage
- Match / correlate system symptoms with likely problems
- Estimate throughput and identify bottlenecks in a system including networking
The following is a partial list of the used files, terms and utilities:
- iostat
- netstat
- w
- top
- sar
- processes blocked on I/O
- blocks out
- vmstat
- pstree, ps
- Isof
- uptime
- swap
- blocks in
Computers hang, People Nags and Applications run with lags. Handling all of this problems is on administrators' shoulders. It doesn't matter if we are talking about a single computer or we are some where in the cloud. We need some tools to explore the behavior of a system in order to find a solution. Performance problems have two main roots, Sometimes lack of system resources such as CPU, Memory, HDD or even Network cause them, Sometimes we as humankind make mistakes. When there is a paradox between what we expect, what is in need and how we configure computers hang.
RAM is like a gateway of a town, everything goes through RAM. If we have a process, it should be loaded in RAM first inorder to be served by CPU later. CPU feeds its Caches from RAM data. How about User activities? If user ask to read some data From HardDisk it is loaded in RAM and then user can work with that.
As it seeam RAM is pretty busy and always in need.Linux uses some Techniques to over come problem, to make it simple lets explain Memory Terminology
| Item | Description |
|---|---|
| Page | The blocks that are used in memory, Ususally 4K size |
| Paging | Used to get memory from secondary storage to primary storage |
| Swap | emulated memory on HDD |
| Virtual Memory | Total allocatable memory, [known as process address space]Linux supports Tera Bytes of virtual memory and use TLB to allocate physial memory. |
| Translation Look aside Buffer(TLB) | Kind of cache which speedup translation between RAM and virtual memory, stored in RAM |
| Page cache | Recently used memory pages are stored here(not cpu cache ) Used for parked data |
| Dirty Cache | Data which are waiting to go to HDD from RAM(Works Like a buffer) |
| Buffers | Used for some Block devices and cache file system metadata.not really important |
Lets explorer whats going inside with some tools and commands.
root@server1:~# vmstat
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
2 0 98012 79256 12136 319060 4 17 170 93 85 174 4 1 95 0 0
the command vmstat show virtual memory status and some other information. For periodic check with interval you can use vmstat 2 5. Lets try free command:
root@server1:~# free -h
total used free shared buff/cache available
Mem: 971M 637M 93M 36M 241M 116M
Swap: 1.0G 403M 617M
if you use -h option you can see human readable values, you can use -m for megabyte and -g for gigabyte view.
as you can see 241M is allocated to buff/cache. to clear buff/cache:
echo 3 > /proc/sys/vm/drop_caches ; free -h
this system just has 1 GigaByte of Ram, so obviously it starts using swap, Whats swappiness?
Swappiness is the kernel parameter that defines how much (and how often) your Linux kernel will copy RAM contents to swap. This parameter's default value is “60” and it can take anything from “0” to “100”. The higher the value of the swappiness parameter, the more aggressively your kernel will swap.
root@server1:~# cd /proc/sys/vm/
root@server1:/proc/sys/vm# cat swappiness
60
root@server1:/proc/sys/vm# echo 90 > swappiness
Monitor and measure the load that you have put on your system by uptime command:
root@server1:~# uptime
06:05:24 up 7:02, 1 user, load average: 0.85, 1.04, 1.08
uptime command shows uptime obviously :), number of current logged users, and Load average in last 1 min, Last 5 min and last 15 min.The way that uptime calculate system load average is base on CPU Load average and Disk I/O.But the way it shows Load Average is base on # of CPU cores. So to find out % of Real System Load we need some calculations:
(Load average / number of cpu cores) x 100 ===> %real load average in our system
so if you are going beyond your CPU capability.You need to investigate more. Sometimes CPU is the bottleneck and some times Disk is bottleneck. top command is here to help us :
top - 05:06:59 up 6:04, 1 user, load average: 0.44, 0.16, 0.05
Tasks: 239 total, 3 running, 236 sleeping, 0 stopped, 0 zombie
%Cpu(s): 98.9 us, 1.1 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 994868 total, 77944 free, 594552 used, 322372 buff/cache
KiB Swap: 1045500 total, 571124 free, 474376 used. 180436 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
8738 root 20 0 7480 96 0 R 93.0 0.0 0:26.89 stress
7478 myuser 20 0 884192 110216 48640 S 4.7 11.1 4:01.21 oxide-rend+
1 root 20 0 185136 3436 2300 S 0.0 0.3 0:03.40 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.01 kthreadd
4 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:+
6 root 20 0 0 0 0 S 0.0 0.0 0:04.64 ksoftirqd/0
7 root 20 0 0 0 0 R 0.0 0.0 0:04.30 rcu_sched
8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_bh
9 root rt 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
10 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 lru-add-dr+
11 root rt 0 0 0 0 S 0.0 0.0 0:00.10 watchdog/0
12 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuhp/0
13 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kdevtmpfs
14 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 netns
15 root 20 0 0 0 0 S 0.0 0.0 0:00.09 khungtaskd
16 root 20 0 0 0 0 S 0.0 0.0 0:00.00 oom_reaper
17 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 writeback
top command gives us information about system uptime, load avarage, and detailed info about processes. top also has some tricks:
| Key | Description |
|---|---|
| press "1" | shows all cpu cores load |
| "shift" + "<" or ">" | sort top based on different culoms |
| "shift" + "p" | sort based CPU usage |
| "shift" + "m" | sort based memory usage |
| press "c" | shows absolute patch of process |
| press "z" | will running process in color |
| press "d" and then delay number | by default top command runs every 3.0 second |
| press "k" and insetr PID of process | Kill the process by using PID |
| press "r" and PID of process | to renice a process |
| "shift" + "w" | ro write top command results |
| press "q" | to exit |
So top command is usefull for monitoring both CPU and RAM and also show us I/O wait processes.For more detailed lets take a look at third line of top command result. Linux has two Spaces from OS point of view, User space and System space , top command classified process this way :
us:% CPU time spent in user space #####Linux has two Spaces from OS point of view, User space and Kernel space
sy:% CPU time spent in kernel space####
ni:% CPU time spent on low priority processes
id:% CPU time spent idle
wa:io wait cpu time (or) % CPU time spent in wait (on disk)####### IO WAIT ######
hi: % CPU time spent servicing/handling hardware interrupts
si:% CPU time spent servicing/handling software interrupts
st:% CPU time in involuntary wait by virtual cpu while hypervisor is servicing another processor
did you see wa? it shows IO wait processes and it happens when the bottleneck is Disk. In this condition a process needs some data to be read from the Hard Disk, but Hard Disk is pretty busy and can not read Data When is needed. So poor process must be waited till Disk dose its jobs. Process is I/O Blocked and sleep :) from CPU point of view process goes in an "Unintrruptable Sleep".This Condition is so bad because we can't even kill that process :( so monitor processes with top command and always make sure that % of I/O waited process is Zero.
If finally we have detected that the problem is Disk speed, We should monitor Disk I/O, top command is amazing but we need to know what program has caused the problem. we use iotop [need to be installed based on your distro, kernel >= 2.6 ]:
Total DISK READ : 805.10 B/s | Total DISK WRITE : 43.24 K/s
Actual DISK READ: 805.10 B/s | Actual DISK WRITE: 34.59 K/s
TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
343 be/3 root 0.00 B/s 5.50 K/s 0.00 % 0.08 % [jbd2/sda1-8]
3399 be/4 payam 0.00 B/s 2.36 K/s 0.00 % 0.05 % firefox [~M Worker]
3344 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.01 % [kworker/u256:0]
3539 be/4 _apt 0.00 B/s 35.38 K/s 0.00 % 0.00 % http
1894 be/4 payam 805.10 B/s 0.00 B/s 0.06 % 0.00 % ibus-ui-gtk3
1 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % init auto noprompt
2 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kthreadd]
4 be/0 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kworker/0:0H]
2053 be/4 payam 0.00 B/s 0.00 B/s 0.00 % 0.00 % indicator~e [gdbus]
6 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [ksoftirqd/0]
7 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [rcu_sched]
8 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [rcu_bh]
9 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/0]
10 be/0 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [lru-add-drain]
11 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/0]
12 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [cpuhp/0]
13 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [cpuhp/1]
14 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/1]
15 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/1]
16 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [ksoftirqd/1]
18 be/0 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kworker/1:0H
There is another tool which gives us less info but its quick and handy, Like vmstat that we have talked about, we have iostat which gives us a snap shot of current situation of Disk I/O: [iostat is a part of sysstat package and need to be installed]:
root@server1:~# iostat
Linux 4.10.0-28-generic (server1) 11/29/2017 _x86_64_ (4 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
2.95 4.12 8.76 1.46 0.00 82.72
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 126.67 2487.11 5265.57 3756449 7952952
There is another tool which is sar, yes that is funny because that is the name of a bird in Farsi :) but here it is acronym for "System Activity Report". For running sar command you should define delay and time for it:
root@server1:~# sar 1 7
Linux 4.10.0-28-generic (server1) 11/29/2017 _x86_64_ (4 CPU)
12:26:42 AM CPU %user %nice %system %iowait %steal %idle
12:26:43 AM all 0.25 0.00 0.00 0.00 0.00 99.75
12:26:44 AM all 0.76 0.00 0.25 0.00 0.00 98.99
12:26:45 AM all 0.50 0.00 0.50 0.00 0.00 99.00
12:26:46 AM all 0.50 0.00 0.75 0.00 0.00 98.74
12:26:47 AM all 0.51 0.00 0.51 0.00 0.00 98.99
12:26:48 AM all 0.50 0.00 0.25 0.00 0.00 99.25
12:26:49 AM all 0.75 0.00 0.75 0.00 0.00 98.49
Average: all 0.54 0.00 0.43 0.00 0.00 99.03
Some times we need to know what files are opened in out system. Weather we have performance issue or just for monitoring whats going on before rebooting the computer. lsof gives us " LiSt of Open Files" :
COMMAND PID TID USER FD TYPE DEVICE SIZE/OFF NODE NAME
systemd 1 root cwd DIR 8,1 4096 2 /
systemd 1 root rtd DIR 8,1 4096 2 /
systemd 1 root txt REG 8,1 1577232 135885 /lib/systemd/systemd
systemd 1 root mem REG 8,1 18976 136484 /lib/x86_64-linux-gnu/libuuid.so.1.3.0
systemd 1 root mem REG 8,1 262408 136292 /lib/x86_64-linux-gnu/libblkid.so.1.1.0
systemd 1 root mem REG 8,1 14608 136324 /lib/x86_64-linux-gnu/libdl-2.23.so
systemd 1 root mem REG 8,1 456632 136429 /lib/x86_64-linux-gnu/libpcre.so.3.13.2
systemd 1 root mem REG 8,1 1868984 136300 /lib/x86_64-linux-gnu/libc-2.23.so
systemd 1 root mem REG 8,1 138696 136446 /lib/x86_64-linux-gnu/libpthread-2.23.so
systemd 1 root mem REG 8,1 286824 136376 /lib/x86_64-linux-gnu/libmount.so.1.1.0
systemd 1 root mem REG 8,1 64144 136282 /lib/x86_64-linux-gnu/libapparmor.so.1.4.0
systemd 1 root mem REG 8,1 92864 136363 /lib/x86_64-linux-gnu/libkmod.so.2.3.0
systemd 1 root mem REG 8,1 117288 136290 /lib/x86_64-linux-gnu/libaudit.so.1.0.0
systemd 1 root mem REG 8,1 55904 136416 /lib/x86_64-linux-gnu/libpam.so.0.83.1
systemd 1 root mem REG 8,1 252152 136457 /lib/x86_64-linux-gnu/libseccomp.so.2.2.3
systemd 1 root mem REG 8,1 31712 136454 /lib/x86_64-linux-gnu/librt-2.23.so
systemd 1 root mem REG 8,1 23128 136303 /lib/x86_64-linux-gnu/libcap.so.2.24
systemd 1 root mem REG 8,1 130224 136458 /lib/x86_64-linux-gnu/libselinux.so.1
systemd 1 root mem REG 8,1 162632 136272 /lib/x86_64-linux-gnu/ld-2.23.so
lsof gives us a very very long list of open files, you can see part of that above. But we usually use it with grep and also we can use it for a specific user lsof -u myuser.
By spreading Internet and growth of personal Networks, the importance of Network grows. When we want explore what has caused problem in network, we should consider whole path, from beginning to the end and visa versa. That is Like talking about car traffic in big cities. Lets get familiar with some commands and tools.
Let add another member to top series commands, iftop. iftop gives you info about Sessions on your NIC and sort them based on transfer rate.
12.5Kb 25.0Kb 37.5Kb 50.0Kb 62.5Kb
└───────────────┴───────────────┴───────────────┴───────────────┴───────────────
192.168.10.131 => ec2-52-35-5-132.us-west-2 444b 1.76Kb 450b
<= 320b 5.51Kb 1.38Kb
192.168.10.131 => ec2-35-162-5-204.us-west- 0b 1.58Kb 405b
<= 0b 5.51Kb 1.38Kb
192.168.10.131 => sof02s18-in-f42.1e100.net 0b 1.33Kb 340b
<= 0b 4.77Kb 1.19Kb
192.168.10.131 => 192.168.10.2 0b 1.87Kb 691b
<= 0b 3.25Kb 0.99Kb
192.168.10.131 => sof02s18-in-f14.1e100.net 0b 494b 123b
<= 0b 696b 174b
192.168.10.131 => 93.184.220.29 0b 768b 192b
<= 0b 0b 0b
192.168.10.131 => a95-101-72-121.deploy.aka 0b 32b 95b
<= 0b 339b 102b
224.0.0.252 => 192.168.10.1 0b 0b 0b
<= 0b 170b 212b
239.255.255.250 => 192.168.10.1 0b 0b 0b
<= 804b 161b 40b
────────────────────────────────────────────────────────────────────────────────
TX: cum: 11.8KB peak: 20.5Kb rates: 444b 7.80Kb 2.24Kb
RX: 28.0KB 62.1Kb 1.10Kb 20.4Kb 5.46Kb
TOTAL: 39.8KB 82.6Kb 1.53Kb 28.2Kb 7.70Kb
Like top, you can use < > keys to sort based on different columns, and you can prees 1 or 2 or 3 inorder to sort based on last 2secs, 10 secs or 40 secs network activities. also you can pick specific Interface by using iftop -i eth1
Networl Load nload is another Handy tool, this time for monitoring current bandwidth.
Device ens33 [192.168.10.131] (1/2):
================================================================================
Incoming:
Curr: 235.20 kBit/s
Avg: 452.10 kBit/s
#|.. Min: 0.00 Bit/s
.| ..#####|. .. ||.| .. Max: 2.56 MBit/s
###.##. .#########| ...... ..|..###|.####| ..||## . Ttl: 35.37 MByte
Outgoing:
Curr: 10.84 kBit/s
Avg: 46.62 kBit/s
Min: 0.00 Bit/s
Max: 370.35 kBit/s
.. Ttl: 1.69 MByte
If you have enjoyed then try ifstat for yourself.
For Testing Connection between two nodes of network we have nice iperf tool.
### MAchine A 192.168.10.131 ### as server###
root@server1:~# iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
[ 4] local 192.168.10.131 port 5001 connected with 192.168.10.130 port 41784
[ ID] Interval Transfer Bandwidth
[ 4] 0.0-10.0 sec 3.44 GBytes 2.95 Gbits/sec
###machine B 192.168.10.130 ### as client ###
iperf -c 192.168.10.131
------------------------------------------------------------
Client connecting to 192.168.10.131, TCP port 5001
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[ 3] local 192.168.10.130 port 41784 connected with 192.168.10.131 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 3.44 GBytes 2.96 Gbits/sec
as both of nodes in my example are virtual machines, you can see amazing 2.95 Gbits/sec bandwidth. Who knows some day in future this might happened in real world :)
And finally, lets introduce a tiny tool to check you internet speed from command line:
apt install speedtest-cli
root@server1:~# speedtest
Retrieving speedtest.net configuration...
Retrieving speedtest.net server list...
Testing from WestHost (107.182.226.165)...
Selecting best server based on latency...
Hosted by Sprint (New York City, NY) [2.13 km]: 581.08 ms
Testing download speed........................................
Download: 1.24 Mbit/s
Testing upload speed..................................................
Upload: 3.23 Mbit/s
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