linux technotes: July 2016

Sunday, July 31, 2016

Yum commands in LINUX

Let’s assume you need to install rpm/package “xorg-x11-apps-7.6-6.el6.x86_64”

[root@tst:/root]4

[root@tst:/root]4 rpm -qa | grep -i xorg-x11-apps-7.6-6.el6.x86_64 >> first step is to grep either the package installed or not .

[root@tst:/root]5 rpm -qa | grep -i xorg-x11-apps* >>if packages was installed with different version it wont show since your checking with particular version .so lets grep with just package name . nothing coming up so it means no package was installed

[root@tst:/root]7 yum install xorg-x11-apps-7.6-6.el6.x86_64 >> when you do yum install package name it will get installed if the package is available in repo.

Loaded plugins: refresh-packagekit, security, ulninfo

Setting up Install Process

Resolving Dependencies

--> Running transaction check

---> Package xorg-x11-apps.x86_64 0:7.6-6.el6 will be installed

--> Finished Dependency Resolution

Dependencies Resolved

============================================================================================================================================================================================================================================

Package Arch Version Repository Size

Installing:

xorg-x11-apps x86_64 7.6-6.el6 oel6_latest_x86_64 276 k

Transaction Summary

Install 1 Package(s)

Total download size: 276 k

Installed size: 705 k

Is this ok [y/N]: y

Downloading Packages:

Running rpm_check_debug

Running Transaction Test

Transaction Test Succeeded

Running Transaction

Installing : xorg-x11-apps-7.6-6.el6.x86_64 1/1

Verifying : xorg-x11-apps-7.6-6.el6.x86_64 1/1

Installed:

xorg-x11-apps.x86_64 0:7.6-6.el6

Complete!

What will happen if packages is not at all installed and we are trying to do yum update with that package name ? see below

[root@tst:/root]6 yum update xorg-x11-apps-7.6-6.el6.x86_64 >> if your trying to do yum update , it won’t installed/update since nothing is already installed . yum update will works only when package was already installed and latest version is available .

Loaded plugins: refresh-packagekit, security, ulninfo

Setting up Update Process

Package(s) xorg-x11-apps-7.6-6.el6.x86_64 available, but not installed.

No Packages marked for Update

what will happen if you do yum install when its already installed ?

[root@tst:/root]8 yum install xorg-x11-apps-7.6-6.el6.x86_64 >> it will say package already installed and latest version .

Loaded plugins: refresh-packagekit, security, ulninfo

Setting up Install Process

Package xorg-x11-apps-7.6-6.el6.x86_64 already installed and latest version

Nothing to do

What will happen if you do yum update with package name ?

[root@tst:/root]9 yum update xorg-x11-apps-7.6-6.el6.x86_64 >> you can see here , when you do yum update its getting updated it means package was installed but its not latest and its getting updated to latest version .

Loaded plugins: refresh-packagekit, security, ulninfo

Setting up Update Process

Resolving Dependencies

--> Running transaction check

---> Package xorg-x11-apps.x86_64 0:7.6-6.el6 will be updated

---> Package xorg-x11-apps.x86_64 0:7.7-6.el6 will be an update

--> Finished Dependency Resolution

Dependencies Resolved

Package Arch Version Repository Size

Updating:

xorg-x11-apps x86_64 7.7-6.el6 ol6_latest_x86_64 276 k

Transaction Summary

Upgrade 1 Package(s)

Total download size: 276 k

Is this ok [y/N]: y

Downloading Packages:

Running rpm_check_debug

Running Transaction Test

Transaction Test Succeeded

Running Transaction

Updating : xorg-x11-apps-7.7-6.el6.x86_64 1/2

Cleanup : xorg-x11-apps-7.6-6.el6.x86_64 2/2

Verifying : xorg-x11-apps-7.7-6.el6.x86_64 1/2

Verifying : xorg-x11-apps-7.6-6.el6.x86_64 2/2

Updated:

xorg-x11-apps.x86_64 0:7.7-6.el6

Complete!

What will happen if you do yum update when package is already latest version ?

[root@tst:/root]12 yum update xorg-x11-apps >> it will show as nothing marked to update . it means no new versions are available already package is to latest version .

Loaded plugins: refresh-packagekit, security, ulninfo

Setting up Update Process

No Packages marked for Update

What will happen if you do yum install if its already installed ?

[root@tst:/root]13 yum install xorg-x11-apps-7.7-6.el6.x86_64

Loaded plugins: refresh-packagekit, security, ulninfo

Setting up Install Process

Package xorg-x11-apps-7.7-6.el6.x86_64 already installed and latest version

Nothing to do

Now let’s do remove the package and see other scenarios ..

[root@tst:/root]14 yum remove xorg-x11-apps-7.7-6.el6.x86_64

Loaded plugins: refresh-packagekit, security, ulninfo

Setting up Remove Process

Resolving Dependencies

--> Running transaction check

---> Package xorg-x11-apps.x86_64 0:7.7-6.el6 will be erased

--> Finished Dependency Resolution

Dependencies Resolved

Package Arch Version Repository Size

Removing:

xorg-x11-apps x86_64 7.7-6.el6 @ol6_latest_x86_64 704 k

Transaction Summary

Remove 1 Package(s)

Installed size: 704 k

Is this ok [y/N]: y

Downloading Packages:

Running rpm_check_debug

Running Transaction Test

Transaction Test Succeeded

Running Transaction

Erasing : xorg-x11-apps-7.7-6.el6.x86_64 1/1

Verifying : xorg-x11-apps-7.7-6.el6.x86_64 1/1

Removed:

xorg-x11-apps.x86_64 0:7.7-6.el6

Complete!

Lets do yum install with bit older version

[root@tst:/root]15 yum install xorg-x11-apps-7.6-6.el6.x86_64

Loaded plugins: refresh-packagekit, security, ulninfo

Setting up Install Process

Resolving Dependencies

--> Running transaction check

---> Package xorg-x11-apps.x86_64 0:7.6-6.el6 will be installed

--> Finished Dependency Resolution

Dependencies Resolved

Package Arch Version Repository Size

Installing:

xorg-x11-apps x86_64 7.6-6.el6 ol6_latest_x86_64 276 k

Transaction Summary

Install 1 Package(s)

Total download size: 276 k

Installed size: 705 k

Is this ok [y/N]: y

Downloading Packages:

Running rpm_check_debug

Running Transaction Test

Transaction Test Succeeded

Running Transaction

Installing : xorg-x11-apps-7.6-6.el6.x86_64 1/1

Verifying : xorg-x11-apps-7.6-6.el6.x86_64 1/1

Installed:

xorg-x11-apps.x86_64 0:7.6-6.el6

ok so package was installed but as we know its bit older version and latest version is available in repo . then what will happen if we do just yum update ?

Complete!

[root@tst:/root]16 yum update >> you can see below “xorg” package getting updated though we didn’t mention about the package name . it means when we do yum update it will update all the packages to latest version as available in our repo .

Loaded plugins: refresh-packagekit, security, ulninfo

Setting up Update Process

Resolving Dependencies

--> Running transaction check

---> Package xorg-x11-apps.x86_64 0:7.6-6.el6 will be updated

---> Package xorg-x11-apps.x86_64 0:7.7-6.el6 will be an update

--> Finished Dependency Resolution

Dependencies Resolved

Package Arch Version Repository Size

Updating:

xorg-x11-apps x86_64 7.7-6.el6 ol6_latest_x86_64 276 k

Transaction Summary

Upgrade 1 Package(s)

Total download size: 276 k

Is this ok [y/N]: y

Downloading Packages:

Running rpm_check_debug

Running Transaction Test

Transaction Test Succeeded

Running Transaction

Updating : xorg-x11-apps-7.7-6.el6.x86_64 1/2

Cleanup : xorg-x11-apps-7.6-6.el6.x86_64 2/2

Verifying : xorg-x11-apps-7.7-6.el6.x86_64 1/2

Verifying : xorg-x11-apps-7.6-6.el6.x86_64 2/2

Updated:

xorg-x11-apps.x86_64 0:7.7-6.el6

Complete!

[root@tst:/root]17

Hope this helps you on how to you use yum . comment below for anything .

Sunday, July 17, 2016

MEMORY USAGE CHECK IN LINUX SYSTEMS

we can check free memory in many ways . Below are the couple of examples on how we can check .

1) free command :-

using free command it gives current total memory allocated and current usage including cache/buffer memory usage .

[root@tstvm ~]# free -m
total used free shared buffers cached
Mem: 988 194 794 0 43 49
-/+ buffers/cache: 101 887
Swap: 1983 0 1983

[root@tstvm ~]#

from the above example

988 gb = total memory allocated

194 gb = current used memory

794 gb = current free memory

43 and 49 is buffer/cache memory .

NOTE:- Linux uses free memory for buffer/cache to keep data read/write from/to disks in memory for speed access in the future.These memory can be reclaimed in case kernel/application needs to allocation explicitly.

2) cat /proc/meminfo

[root@tstvm ~]# cat /proc/meminfo

MemTotal: 1012548 kB

MemFree: 813080 kB

Buffers: 44428 kB

Cached: 50812 kB

SwapCached: 0 kB

Active: 67108 kB

Inactive: 44864 kB

Active(anon): 16968 kB

Inactive(anon): 4 kB

Active(file): 50140 kB

Inactive(file): 44860 kB

Unevictable: 0 kB

Mlocked: 0 kB

SwapTotal: 2031608 kB

SwapFree: 2031608 kB

Dirty: 8 kB

Writeback: 0 kB

AnonPages: 16752 kB

Mapped: 11060 kB

Shmem: 236 kB

Slab: 64652 kB

SReclaimable: 12612 kB

SUnreclaim: 52040 kB

KernelStack: 776 kB

PageTables: 2912 kB

NFS_Unstable: 0 kB

Bounce: 0 kB

WritebackTmp: 0 kB

CommitLimit: 2537880 kB

Committed_AS: 103460 kB

VmallocTotal: 34359738367 kB

VmallocUsed: 276296 kB

VmallocChunk: 34359446148 kB

HardwareCorrupted: 0 kB

AnonHugePages: 0 kB

HugePages_Total: 0

HugePages_Free: 0

HugePages_Rsvd: 0

HugePages_Surp: 0

Hugepagesize: 2048 kB

DirectMap4k: 6144 kB

DirectMap2M: 1042432 kB

DirectMap1G: 0 kB

[root@tstvm ~]#

Active memory is the amount of buffer and cache memory has been recently used, which is not usually reclaimed

Inactive memory is the amount of buffer and cache memory that has not been recently used, can be reclaimed by kernel

3) TOP command :-

using top command you can see memory/cpu usage including the current running process. you can the each process and that perticular process memory/cpu usage .

top - 07:48:08 up 21 min, 1 user, load average: 0.00, 0.00, 0.02

Tasks: 89 total, 1 running, 88 sleeping, 0 stopped, 0 zombie

Cpu(s): 0.0%us, 0.3%sy, 0.0%ni, 99.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st

Mem: 1012548k total, 199864k used, 812684k free, 44456k buffers

Swap: 2031608k total, 0k used, 2031608k free, 51072k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND

1 root 20 0 19356 1524 1224 S 0.0 0.2 0:01.71 init

2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd

3 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0

4 root 20 0 0 0 0 S 0.0 0.0 0:00.01 ksoftirqd/0

5 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0

6 root RT 0 0 0 0 S 0.0 0.0 0:00.01 watchdog/0

7 root 20 0 0 0 0 S 0.0 0.0 0:02.26 events/0

8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cgroup

9 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khelper

10 root 20 0 0 0 0 S 0.0 0.0 0:00.00 netns

11 root 20 0 0 0 0 S 0.0 0.0 0:00.00 async/mgr

12 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pm

13 root 20 0 0 0 0 S 0.0 0.0 0:00.01 sync_supers

14 root 20 0 0 0 0 S 0.0 0.0 0:00.01 bdi-default

15 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kintegrityd/0

16 root 20 0 0 0 0 S 0.0 0.0 0:00.20 kblockd/0

17 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpid

18 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpi_notify

19 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpi_hotplug

20 root 20 0 0 0 0 S 0.0 0.0 0:00.03 ata/0

21 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ata_aux

22 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksuspend_usbd

23 root 20 0 0 0 0 S 0.0 0.0 0:00.17 khubd

24 root 20 0 0 0 0 S 0.0 0.0 0:00.02 kseriod

25 root 20 0 0 0 0 S 0.0 0.0 0:00.00 md/0

26 root 20 0 0 0 0 S 0.0 0.0 0:00.00 md_misc/0

27 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khungtaskd

28 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kswapd0

29 root 25 5 0 0 0 S 0.0 0.0 0:00.00 ksmd

30 root 39 19 0 0 0 S 0.0 0.0 0:00.00 khugepaged

31 root 20 0 0 0 0 S 0.0 0.0 0:00.00 aio/0

32 root 20 0 0 0 0 S 0.0 0.0 0:00.00 crypto/0

37 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthrotld/0

38 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pciehpd

40 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kpsmoused

41 root 20 0 0 0 0 S 0.0 0.0 0:00.00 usbhid_resumer

72 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kstriped

Top Command Analysis :-

Top is the command which gives system resources details

root@localhost linuxtechnotes]# top
top - 13:31:20 up 1:37, 3 users, load average: 0.00, 0.00, 0.00

System is uptine is 1 hour 37ms and current time is 13.31 and current user logined is 3

load average gives 3 time intervals which are 1,5,15ms interval

As above load average last 1min load is 0% at last 5ms load is 0% and last 15ms load is 0%

Shift+m will give based on top memory utilizatoin
shift +p willl give based on top cpu utilization

NI is nice value like priority for system resources to use

-20 to +19

-20 is top and 19 is lowest priority which means lowest value have highest priority and highest value have lower priority

To chnage the process priority use r option
r and then give process id then hit enter
its aks renice pid value then can give as needed

%mem is % usage of memory that process using.for ex if its 90% process is using 90% of memory
%cpu is %usage of cpu that process using. for ex if its 200% it means that process is using 2 cores of cpu

what is 404 error in linux ?

404 error is a normal error that the webpage/URL you were trying to reach could not be found on the server. It is a Client-side error which means that either the page has been removed or moved and the URL was not changed accordingly, or that you typed in the URL incorrectly.

for example below webpage has been removed and no longer exist.

if your trying to access the above webpage you will get 404 error .

same kind of 404 eror in linux you will get when your trying to access http url and yum repository .

lets say you get this error when your trying to run any "yum" command it means the repo URL which setup in your repository is no longer exists .

What commands do you use to check free memory on the linux system ?

from the above example

988 gb = total memory allocated

194 gb = current used memory

794 gb = current free memory

43 and 49 is buffer/cache memory .

2) cat /proc/meminfo

[root@tstvm ~]# cat /proc/meminfo

MemTotal: 1012548 kB

MemFree: 813080 kB

Buffers: 44428 kB

Cached: 50812 kB

SwapCached: 0 kB

Active: 67108 kB

Inactive: 44864 kB

Active(anon): 16968 kB

Inactive(anon): 4 kB

Active(file): 50140 kB

Inactive(file): 44860 kB

Unevictable: 0 kB

Mlocked: 0 kB

SwapTotal: 2031608 kB

SwapFree: 2031608 kB

Dirty: 8 kB

Writeback: 0 kB

AnonPages: 16752 kB

Mapped: 11060 kB

Shmem: 236 kB

Slab: 64652 kB

SReclaimable: 12612 kB

SUnreclaim: 52040 kB

KernelStack: 776 kB

PageTables: 2912 kB

NFS_Unstable: 0 kB

Bounce: 0 kB

WritebackTmp: 0 kB

CommitLimit: 2537880 kB

Committed_AS: 103460 kB

VmallocTotal: 34359738367 kB

VmallocUsed: 276296 kB

VmallocChunk: 34359446148 kB

HardwareCorrupted: 0 kB

AnonHugePages: 0 kB

HugePages_Total: 0

HugePages_Free: 0

HugePages_Rsvd: 0

HugePages_Surp: 0

Hugepagesize: 2048 kB

DirectMap4k: 6144 kB

DirectMap2M: 1042432 kB

DirectMap1G: 0 kB

[root@tstvm ~]#

Active memory is the amount of buffer and cache memory has been recently used, which is not usually reclaimed

Inactive memory is the amount of buffer and cache memory that has not been recently used, can be reclaimed by kernel

3) TOP command :-

using top command you can see memory/cpu usage including the current running process. you can the each process and that perticular process memory/cpu usage .

top - 07:48:08 up 21 min, 1 user, load average: 0.00, 0.00, 0.02

Tasks: 89 total, 1 running, 88 sleeping, 0 stopped, 0 zombie

Cpu(s): 0.0%us, 0.3%sy, 0.0%ni, 99.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st

Mem: 1012548k total, 199864k used, 812684k free, 44456k buffers

Swap: 2031608k total, 0k used, 2031608k free, 51072k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND

1 root 20 0 19356 1524 1224 S 0.0 0.2 0:01.71 init

2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd

3 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0

4 root 20 0 0 0 0 S 0.0 0.0 0:00.01 ksoftirqd/0

5 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0

6 root RT 0 0 0 0 S 0.0 0.0 0:00.01 watchdog/0

7 root 20 0 0 0 0 S 0.0 0.0 0:02.26 events/0

8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cgroup

9 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khelper

10 root 20 0 0 0 0 S 0.0 0.0 0:00.00 netns

11 root 20 0 0 0 0 S 0.0 0.0 0:00.00 async/mgr

12 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pm

13 root 20 0 0 0 0 S 0.0 0.0 0:00.01 sync_supers

14 root 20 0 0 0 0 S 0.0 0.0 0:00.01 bdi-default

15 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kintegrityd/0

16 root 20 0 0 0 0 S 0.0 0.0 0:00.20 kblockd/0

17 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpid

18 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpi_notify

19 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpi_hotplug

20 root 20 0 0 0 0 S 0.0 0.0 0:00.03 ata/0

21 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ata_aux

22 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksuspend_usbd

23 root 20 0 0 0 0 S 0.0 0.0 0:00.17 khubd

24 root 20 0 0 0 0 S 0.0 0.0 0:00.02 kseriod

25 root 20 0 0 0 0 S 0.0 0.0 0:00.00 md/0

26 root 20 0 0 0 0 S 0.0 0.0 0:00.00 md_misc/0

27 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khungtaskd

28 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kswapd0

29 root 25 5 0 0 0 S 0.0 0.0 0:00.00 ksmd

30 root 39 19 0 0 0 S 0.0 0.0 0:00.00 khugepaged

31 root 20 0 0 0 0 S 0.0 0.0 0:00.00 aio/0

32 root 20 0 0 0 0 S 0.0 0.0 0:00.00 crypto/0

37 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthrotld/0

38 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pciehpd

40 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kpsmoused

41 root 20 0 0 0 0 S 0.0 0.0 0:00.00 usbhid_resumer

72 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kstriped