5 commands to check memory usage on Linux

Memory Usage

On linux, there are commands for almost everything, because the gui might not be always available. When working on servers only shell access is available and everything has to be done from these commands. So today we shall be checking the commands that can be used to check memory usage on a linux system. Memory include RAM and swap.

It is often important to check memory usage and memory used per process on servers so that resources do not fall short and users are able to access the server. For example a website. If you are running a webserver, then the server must have enough memory to serve the visitors to the site. If not, the site would become very slow or even go down when there is a traffic spike, simply because memory would fall short. Its just like what happens on your desktop PC.

1. free command

The free command is the most simple and easy to use command to check memory usage on linux. Here is a quick example

$ free -m
             total       used       free     shared    buffers     cached
Mem:          7976       6459       1517          0        865       2248
-/+ buffers/cache:       3344       4631
Swap:         1951          0       1951

The m option displays all data in MBs. The total os 7976 MB is the total amount of RAM installed on the system, that is 8GB. The used column shows the amount of RAM that has been used by linux, in this case around 6.4 GB. The output is pretty self explanatory. The catch over here is the cached and buffers column. The second line tells that 4.6 GB is free. This is the free memory in first line added with the buffers and cached amount of memory.

Linux has the habit of caching lots of things for faster performance, so that memory can be freed and used if needed.
The last line is the swap memory, which in this case is lying entirely free.

2. /proc/meminfo

The next way to check memory usage is to read the /proc/meminfo file. Know that the /proc file system does not contain real files. They are rather virtual files that contain dynamic information about the kernel and the system.

$ cat /proc/meminfo
MemTotal:        8167848 kB
MemFree:         1409696 kB
Buffers:          961452 kB
Cached:          2347236 kB
SwapCached:            0 kB
Active:          3124752 kB
Inactive:        2781308 kB
Active(anon):    2603376 kB
Inactive(anon):   309056 kB
Active(file):     521376 kB
Inactive(file):  2472252 kB
Unevictable:        5864 kB
Mlocked:            5880 kB
SwapTotal:       1998844 kB
SwapFree:        1998844 kB
Dirty:              7180 kB
Writeback:             0 kB
AnonPages:       2603272 kB
Mapped:           788380 kB
Shmem:            311596 kB
Slab:             200468 kB
SReclaimable:     151760 kB
SUnreclaim:        48708 kB
KernelStack:        6488 kB
PageTables:        78592 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     6082768 kB
Committed_AS:    9397536 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      420204 kB
VmallocChunk:   34359311104 kB
HardwareCorrupted:     0 kB
AnonHugePages:         0 kB                                                                                                                           
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:       62464 kB
DirectMap2M:     8316928 kB
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Check the values of MemTotal, MemFree, Buffers, Cached, SwapTotal, SwapFree.
They indicate same values of memory usage as the free command.

3. vmstat

The vmstat command with the s option, lays out the memory usage statistics much like the proc command. Here is an example

$ vmstat -s
      8167848 K total memory
      7449376 K used memory
      3423872 K active memory
      3140312 K inactive memory
       718472 K free memory
      1154464 K buffer memory
      2422876 K swap cache
      1998844 K total swap
            0 K used swap
      1998844 K free swap
       392650 non-nice user cpu ticks
         8073 nice user cpu ticks
        83959 system cpu ticks
     10448341 idle cpu ticks
        91904 IO-wait cpu ticks
            0 IRQ cpu ticks
         2189 softirq cpu ticks
            0 stolen cpu ticks
      2042603 pages paged in
      2614057 pages paged out
            0 pages swapped in
            0 pages swapped out
     42301605 interrupts
     94581566 CPU context switches
   1382755972 boot time
         8567 forks
$

The top few lines indicate total memory, free memory etc and so on.

4. top command

The top command is generally used to check memory and cpu usage per process. However it also reports total memory usage and can be used to monitor the total RAM usage. The header on output has the required information. Here is a sample output

top - 15:20:30 up  6:57,  5 users,  load average: 0.64, 0.44, 0.33
Tasks: 265 total,   1 running, 263 sleeping,   0 stopped,   1 zombie
%Cpu(s):  7.8 us,  2.4 sy,  0.0 ni, 88.9 id,  0.9 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:   8167848 total,  6642360 used,  1525488 free,  1026876 buffers
KiB Swap:  1998844 total,        0 used,  1998844 free,  2138148 cached

  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND                                                                                 
 2986 enlighte  20   0  584m  42m  26m S  14.3  0.5   0:44.27 yakuake                                                                                 
 1305 root      20   0  448m  68m  39m S   5.0  0.9   3:33.98 Xorg                                                                                    
 7701 enlighte  20   0  424m  17m  10m S   4.0  0.2   0:00.12 kio_thumbnail

Check the KiB Mem and KiB Swap lines on the header. They indicate total, used and free amounts of the memory. The buffer and cache information is present here too, like the free command.

5. htop

Similar to the top command, the htop command also shows memory usage along with various other details.

htop-memory-ram-usage

The header on top shows cpu usage along with RAM and swap usage with the corresponding figures.

RAM Information

To find out hardware information about the installed RAM, use the demidecode command. It reports lots of information about the installed RAM memory.

$ sudo dmidecode -t 17
# dmidecode 2.11
SMBIOS 2.4 present.

Handle 0x0015, DMI type 17, 27 bytes
Memory Device
        Array Handle: 0x0014
        Error Information Handle: Not Provided
        Total Width: 64 bits
        Data Width: 64 bits
        Size: 2048 MB
        Form Factor: DIMM
        Set: None
        Locator: J1MY
        Bank Locator: CHAN A DIMM 0
        Type: DDR2
        Type Detail: Synchronous
        Speed: 667 MHz
        Manufacturer: 0xFF00000000000000
        Serial Number: 0xFFFFFFFF
        Asset Tag: Unknown
        Part Number: 0x524D32474235383443412D36344643FFFFFF

Provided information includes the size (2048MB), type (DDR2) , speed(667 Mhz) etc.

Summary

All the above mentioned commands work from the terminal and do not have a gui. When working on a desktop with a gui, it is much easier to use a GUI tool with graphical output. The most common tools are gnome-system-monitor on gnome and ksysguard on KDE. Both provide resource usage information about cpu, ram, swap and network bandwidth in a graphical and easy to understand visual output.

CentOS Web Panel – Installation

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Now you are ready to start CWP Installation
CWP installer can run more than 30 minutes, because it needs to compile apache and php from source.

We have CWP installation with default CentOS MySQL version 5.1 and the latest MariaDB as additional option.

Installer with MySQL version 5.1

cd /usr/local/src
wget http://centos-webpanel.com/cwp-latest
sh cwp-latest

Installer with MARIA-DB 10.1.10

cd /usr/local/src
wget http://centos-webpanel.com/cwp-latest
sh cwp-latest -d mariadb

If download link doesn’t work then you can use the following: http://dl1.centos-webpanel.com/files/cwp-latest

Reboot Server
Reboot your server so that all updates can take affect and to start CWP.

reboot

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If you hosted with us, you can use the dns setting for your domain name server pointing for result worldwide.

Free & Public DNS Servers

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Your ISP automatically assigns DNS servers when your router or computer connects to the Internet via DHCP… but you don’t have to use those.

Below are free DNS servers you can use instead of the ones assigned, the best and most reliable of which, from the likes of Google and OpenDNS, you can find below:

Free & Public DNS Servers (Valid March 2016)

Provider Primary DNS Server Secondary DNS Server
Level31 209.244.0.3 209.244.0.4
Verisign2 64.6.64.6 64.6.65.6
Google3 8.8.8.8 8.8.4.4
DNS.WATCH4 84.200.69.80 84.200.70.40
Comodo Secure DNS 8.26.56.26 8.20.247.20
OpenDNS Home5 208.67.222.222 208.67.220.220
DNS Advantage 156.154.70.1 156.154.71.1
Norton ConnectSafe6 199.85.126.10 199.85.127.10
GreenTeamDNS7 81.218.119.11 209.88.198.133
SafeDNS8 195.46.39.39 195.46.39.40
OpenNIC9 50.116.23.211 192.99.240.129
SmartViper 208.76.50.50 208.76.51.51
Dyn 216.146.35.35 216.146.36.36
FreeDNS10 37.235.1.174 37.235.1.177
Alternate DNS11 198.101.242.72 23.253.163.53
Yandex.DNS12 77.88.8.8 77.88.8.1
censurfridns.dk13 89.233.43.71 91.239.100.100
Hurricane Electric14 74.82.42.42
puntCAT15 109.69.8.51

Note: Primary DNS servers are sometimes called preferred DNS servers and secondary DNS servers are sometimes called alternate DNS servers. Primary and secondary DNS servers can be “mixed and matched” to provide another layer of redundancy.

Why Use Different DNS Servers?

One reason you might want to change from the DNS servers assigned by your ISP is if you suspect there’s a problem with the ones you’re using now.

5th Cloud Name System in testing term

We have setup the 5th location for our cloud base name server system in another Europe datacenter. Currently still on testing terms. If everything goes fine, we will release it for production.

And into production, customer in the Europe can chose to use it also.

5th Location will be located at United Kingdom.

6th Location will be soon be available at Germany.

USA – West Virgina is down due to Network issue

Hello,

There is some problem with our USA – West Virgina Network, the datacenter side is fixing th network issue.

Issue report: 23/03/2016, 19:00 GMT+8

We will update once problem resolved.

Sorry for any inconvenience caused.

Regards,

Network Team

http://www.habangnet.com

—————————————————————————————————

Update Record: Issue was being fully resolve on 24/03/2016, 03:00 GMT+8.

Accident detail: An outage with provider switching equipment in the Equinix Ashburn DC2 facility. The issue at DC2 impacted all service at our West Virginia datacenter. The problem involved Juniper EX switching equipment and took awhile to isolate due to the appearance of all configuration and protocols operating and seeming to be correct.

Please verify that service has been restored to your servers and let us know so that we can proactively assist you in bringing the service back online if it not already restored.

Even though outages like this are rare, we know that they greatly impact your business and we were working our hardest to bring services back online.

Thank you for your business and please let us know if you have any questions or require additional support.

Dallas, TX Network Maintenance

Dallas Customers,

We have received an update from our upstream provider that, there is an upcoming network maintenance that is not expected to cause a network outage, but if issues arise, periodic intermittent outages may occur. The relatively short notice is due to the state of some our network switches presently in a critical state. Our Juniper switches will require a code upgrade to the latest version of Junos OS that is prescribed by JTAC. A possible reboot may be required to ensure all new configurations take effect.

Details –
Date: March 16, 2016
Time: 10:30PM PDT
Duration: Up to 15 minutes
Effect: Intermittent Network Outage
Facilities: Dallas, Texas

If you have any questions about this outage or want more information on how it will relate to your specific services with us, please feel free to reach us at Helpdesk.

Thank you,
Will Low
HaBangNet NOC Team

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If you encounter any issue with your account, please contact support

We schedule the work will start from 10th of March, 2016 and will end by 25th of March, 2016.

Regards,

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CVE-2016-1531 Exim

On Wednesday, March 2, 2016, Exim announced a vulnerability in all versions of the Exim software.

Impact

According to Exim development: “All installations having Exim set-uid root and using ‘perl_startup’ are vulnerable to a local privilege escalation. Any user who can start an instance of Exim (this is normally *any* user) can gain root privileges.”
Releases

The following versions of cPanel & WHM were patched to have the correct version of Exim. All previous versions of cPanel & WHM, including 11.48.x and below, are vulnerable to a set-uid attack on Exim.
11.50 11.50.5.0
11.52 11.52.4.0
11.54 11.54.0.18
EDGE 11.55.9999.106
CURRENT 11.54.0.18
RELEASE 11.54.0.18
STABLE 11.54.0.18

How to determine if your server is up to date

The updated RPMs provided by cPanel will contain a changelog entry with the CVE number. You can check for this changelog entry with the following command:
rpm -q –changelog exim | grep CVE-2016-1531

The output should resemble below:
Fixes CVE-2016-1531
What to do if you are not up to date.

If your server is not running one of the above versions, update immediately.

You can upgrade your server by navigating to WHM Home »cPanel »Upgrade to Latest Version and clicking “Click to Upgrade” (https://documentation.cpanel.net/display/ALD/Update+Preferences)

Alternatively, you can run the below commands to upgrade your server from the command line:
/scripts/upcp
/usr/bin/system-perl scripts/check_cpanel_rpms –fix –long-list

Verify the new Exim RPM was installed:
rpm -q –changelog exim | grep CVE-2016-1531

The output should resemble below:
Fixes CVE-2016-1531

What has changed?

Exim now provides two configuration options which limit what environment variables are available to Exim and all of its child processes. The variables are keep_environment and add_environment. For the initial release with this feature, cPanel will be setting the variables as follows in all supported cPanel & WHM systems. These values can be modified in the Advanced Configuration Editor if necessary, though we advise caution on adding too many variables to keep_environment.

/etc/exim.conf
keep_environment = X-SOURCE : X-SOURCE-ARGS : X-SOURCE-DIR
add_environment = PATH=/usr/local/sbin::/usr/local/bin::/sbin::/bin::/usr/sbin::/usr/bin::/sbin::/bin
Additional Information

CVE: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1531

Initial Public Disclosure: https://lists.exim.org/lurker/message/20160302.191005.a72d8433.en.html

If you are still experiencing issues or need additional help, please contact cPanel support. If you’re hosted a VPS or Dedicated server with us, you do not need to worry, if your was a managed set, we will take care of it. If your wasn’t a managed set, but do need assistant, you can submit a ticket at client portal.

Posted by HaBangNet Team
http://www.habangnet.com