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How to monitor disk performance on RHEL or CentOS 7 ? iotop : Watches I/O usage information output by the Linux kernel (requires 2.6.20 or later) and displays a table of current I/O usage by processes or threads on the system. At least the CONFIG_TASK_DELAY_ACCT, CONFIG_TASK_IO_ACCOUNTING, CONFIG_TASKSTATS and CONFIG_VM_EVENT_COUNTERS options need to be enabled in your Linux kernel build configuration. iotop displays columns for the I/O bandwidth read and written by each process/thread during the sampling period. It also displays the percentage of time the thread/process spent while swapping in and while waiting on I/O. For each process, its I/O priority (class/level) is shown. [root@localhost ~]# iotop Total DISK READ :       0.00 B/s | Total DISK WRITE :       0.00 B/s Actual DISK READ:       0.00 B/s | Actual DISK WRITE:       0.00 B/s    TID  PRIO  USER  ...

How to add more swap space by adding new swap partition in RHEL or CentOS 7 What is swap? Swap space on a disk is used when the amount of physical RAM is full in the Linux system. When the system runs out of RAM, inactive pages are moved from the RAM to the swap space. Swap space can be either a dedicated swap partition or a swap file. So here we will see how you can add more swap space as a swap file. In this article we will see how we can add more swap space using a new swap partition. Steps : Let's check how much swap is available on the system currently: [root@localhost ~]# swapon --show [root@localhost ~]# free -h I have a new 10GB disk named "/dev/sdb" and i want to use it as a swap space. [root@localhost ~]# fdisk -l Disk /dev/sdb: 10.7 GB, 10737418240 bytes, 20971520 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Step 1 : Create a...

How to add more swap space as a swapfile on RHEL or CentOS 7 What is swap? Swap space on a disk is used when the amount of physical RAM is full in the Linux system. When the system runs out of RAM, inactive pages are moved from the RAM to the swap space. Swap space can be either a dedicated swap partition or a swap file. So here we will see how you can add more swap space as a swap file. In this article we will see how we can add more swap space using a swapfile. Steps : Let's check how much swap is available on the system currently: [root@localhost ~]# swapon --show NAME      TYPE      SIZE USED PRIO /dev/dm-1 partition 3.9G    0B   -2 [root@localhost ~]# free -h               total        used        free      shared  buff/cache   available Mem:           3.7G      ...

top : The top provides a dynamic real-time view of running processes, CPU, Memory and SWAP utilization on a system. It can display system summary information as well as a list of processes or threads currently being managed by the Linux kernel. [root@localhost ~]# top In case as a root you want to check it for some particular user then : [root@localhost ~]# top -u hpe pmap : This command report memory map of a process or processes. [root@localhost ~]# pmap -d 22745 vmstat : This command reports information about processes, memory, paging, block IO, traps, disks and cpu activity. [root@localhost ~]# vmstat -w [root@localhost ~]# vmstat -as [root@localhost ~]# vmstat -dw [root@localhost ~]# vmstat -D             5 disks             2 partitions         48470 total reads           104 merged reads     ...

What is Space Reclamation? This feature supports Thin Provisioned environment, and it is the process of freeing space from the storage system that has already been freed from the host file system. A host file system contains metadata to keep track to know which blocks are available to store new data and which blocks contain actual data and must not be overwritten. This metadata is stored within the LUN. When a file is deleted in the host file system, the file system metadata is updated to mark that file's blocks as free space. Total file system free space is then recalculated to include the newly-freed blocks. To the storage system, these metadata updates appear no different than any other writes being performed by the host. Therefore, the storage system is unaware that any deletions have occurred. What is Unmapping? Unmapping is a process which de-allocates relationship between LBA and a physical block in a logical unit. Reclamation within RHEL and CentOS: RHEL / Ce...

/dev/random will block after the entropy pool is exhausted. It will remain blocked until additional data has been collected from the sources of entropy that are available. This can slow down random data generation. Randomness is critical to the security of cryptography in your application – one-time pads, key generation. [root@localhost ~]# dd if=/dev/random of=random.txt bs=2048 count=2048 dd: warning: partial read (82 bytes); suggest iflag=fullblock 0+2048 records in 0+2048 records out 150665 bytes (151 kB) copied, 21.6704 s, 7.0 kB/s /dev/urandom will not block. Instead it will reuse the internal pool to produce more pseudo-random bits. It's best when we have to a large file with random data. Also if you are using "dd" command to wipe data of a disk by replacing it with random data. [root@localhost ~]# dd if=/dev/urandom of=urandom.txt bs=2048 count=2048 2048+0 records in 2048+0 records out 4194304 bytes (4.2 MB) copied, 0.0361976 s, 116 MB/s

/var/log/messages – This file contains global system messages, including the messages that are logged during system startup. There are several things that are logged in /var/log/messages including mail, cron, daemon, kern, auth, etc. [root@localhost ~]# cat /var/log/messages Apr 17 20:30:03 localhost rsyslogd: [origin software="rsyslogd" swVersion="8.24.0-34.el7" x-pid="9423" x-info="http://www.rsyslog.com"] rsyslogd was HUPed Apr 17 20:40:02 localhost systemd: Started Session 9 of user root. Apr 17 20:40:32 localhost dhclient[9217]: DHCPREQUEST on ens33 to 192.168.189.254 port 67 (xid=0xde4e9a7) Apr 17 20:40:32 localhost dhclient[9217]: DHCPACK from 192.168.189.254 (xid=0xde4e9a7) Apr 17 20:40:32 localhost NetworkManager[8908]: <info>  [1555513832.8097] dhcp4 (ens33):   address 192.168.189.128 Apr 17 20:40:32 localhost NetworkManager[8908]: <info>  [1555513832.8107] dhcp4 (ens33):   plen 24 (255.255.255.0) Apr 17 20:40:32 ...

"/dev/zero" and "/dev/null" are two dummy devices files which are useful for creating empty files. "/dev/zero":   It is used to create a file with no data but with required size(A file with all zero’s written on it). Let's create file with /dev/zero [root@localhost ~]# dd if=/dev/zero of=/opt/zero.txt bs=2048 count=2048 2048+0 records in 2048+0 records out 4194304 bytes (4.2 MB) copied, 0.150465 s, 27.9 MB/s it creates a file that has continuous zeros in it. So we can say that /dev/zero is a file which is used to create a new file with some required size without any meaning to the data. "/dev/null": This file is useful in cases like redirecting unwanted output/error etc to this file. Actually it acts as a black hole which absorbs this unwanted input. So whenever you feed some data to this file, you can not retrieve the data which is fed to it. This file even useful for creating files with zero size. e.g. If you see i h...

How to install and configure Docker on RHEL or CentOS 7 ? Step 1. Install the required packages. yum-utils provides the yum-config-manager utility, and device-mapper-persistent-data and lvm2 are required by the device-mapper storage driver. Verify if centos "extras" repository is enabled in "/etc/yum.repos.d/CentOS-Base.repo", bydefault it would be enabled: [ extras ] name=CentOS-$releasever - Extras mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras&infra=$infra #baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7 NOTE:  If installing on RHEL 7.5 or ater version, please mount RHEL 7.6  or later ISO to /mnt and add local repository for yum, note that RHEL 7.6 iso is needed to update few of the packages and dependencies as 7.5 ISO has old version of packages which are not compatible to the latest docker release...