Bogdan Ulea

I have the partition created:
# cat /proc/partitions
Type mkfs and press tab twice.
There are many mkfs utilities. The default is mkfs.xfs.
# mkfs.xfs –help (check the options)
blocksize is for large file syse and need big blocks to alocate.
inode is useful for SELinux in order to store metadata.
label – is a name for fileSystem.
# mkfs.xfs -L myfs /dev/sdb1

Mounting manually
in order to use it, use mount command:
#mount –help
simple option for moment:
#mount /dev/sdb1 /mnt
mounting is connecting something to a directory.
Check by listing all mounted devices:
# mount
Check only my device:
# mount | grep ^/dev
If want to disconnect device:
# umount /dev/sdb1
or use:
# umount /mnt
If I don’t want after next boot to be changed the anme of device from /dev/sdb1 to /dev/sdc1, use UUID
Display UUID:
# blkid (block ID)
UUID is generated and is unique and Label is generated manually by administrator and is fixed.
# mount LABEL=myfs /mnt

Use fstab:
The clasical way to automount:
# /etc/fstab
Every file system have UUID.
# blkid
Mount options. Can be used for ACL the acl mount option on /etc/fstab
Column 5 is the backup support. 1 is the backup support which is used in older environments.
Column 6 is for fsck (fs check) is checking the fs. On boot is checked. Option 0 is for no, 1 is for checking /root filesystem first and 2 is for checking and is not root file system.

Create partition > make file system > mount it.
# vi /etc/fstab
All file systems are added there.
Device name mount point fileSystems default backup checkOnBooting
/dev/sdb1 /data xfs defaults 1 2
Test it:
# mount -a
create the directory /data
# mount -a
verify:
# mount | grep ^/dev/
There are some problems. If the server change the name, the file system will not be mounted. Need the label or the UUID.
# blkid (show labels and UUID for all file systems)
LABEL=myfs /data xfs defaults 1 2
Change the label of file system:
# xfs_admin help
# xfs_admin -L bootdevice /dev/sda1

XFS – Default in RHEL 7. Based on B-tree database. Good tuning options for different workload.
Ext4 – old and is base on ext2 from 1993. Not scalable
Btrfs – (copy-on-write). Future.
vfat – for Windows capabilities.
GFS2 – clustoring on active-active HA Cluster Environments
Gluster – For distributed file systems. Is base on bricks of XFS and is used for clouding.

Add a new virtual disk.
Verify the available space.
# cat /proc/partitions
Into proc directory is all the information about what is happening into kernel.
sdb is the new device used to create partitions.
On sda there are 2 partitions: sda1 and sda2.
Create partitions with fdisk:
# fdisk /dev/sdb
type “m” for help. There is menu. The important are:
“p” print the current layout…partition table
“n” – add a new partition.
“w” – write the information to disk.
use “p” to create partition.
The size of space is 1073 MB which have 2097152 sectors. Every sector is 1/2 KBytes (512 bytes). The sectors will be used for creating partitions on disk
type “n” for new.
!!!!!! Always use “p” for primary partition unless want to create more than 4 partitions on disk.
Choose default by press for type, number and first sector. 1MB is used to store metadata.
Size for last sector. The size +size100M. If not “M”, it will choose automatically as sector and is too small.
Write changes to disk with “w”.
Verify:
# cat /proc/partitions
Now have to create file-system. If there is an error with “device is busy”, reboot the system.

rsyslog – is the old logging system and journald is the new one.
All journald logs are into a binary files.
Systemctl can be used to get the logs.
# systemctl status nfs
# journalctl – show the content of the file
Filtering:
# journalctl -b (boot information).
# journalctl –since=yesterday (all the info since yesterday)
look other server. SLAPD process is log there.
# systemctl status slapd
# systemctl status slapd -l
Journald is getting information from systemctl.
# journalctl -u slapd (all information about a process)
Details about information….VERY GOOD:
# journalctl -u slapd -o verbose
Configuring log rotate.
# cd /etc
# vi logrotate.conf – is the configuration file
# vi logrotate.d – is the directory where are stored logs for packages installed from RPM.
all the information about log rotate should be here:
# vi logrotate.conf
# tail /var/log/secure
# journalctl _COMM=su (check some commands that can be specify)
more information with verbose:
# journalctl _COMM=su -o verbose

Configure log rotate:
# vi /etc/logrotate.conf
rotate 6
No need to restart because is a cron job and the file will be read next time.

Find if CPU support:
# cat /proc/cpuinfo
i’m interested about flags line
Intel base CPU have VMX
# lsmod | grep kvm
There are 2 modules: one from generic linux and another one from specific platform support.
Check the status of libvirtd
# system status libvirtd
Check the link:
# ip link show
This device virbr0 (virtual bridge) is special created for virtualization. Is like an embedded bridge in order to share connection.
To support KVM need 64 bit kernel:
# arch
Support the CPU:
# grep vmx /proc/cpuinfo
Need libvirtd available:
# systemctl status libvirtd
Virtualization shell:
# virsh
After starting the program, type “help” in order to see the list with options.
Basic commands:
List what VM running:
# virsh list
List existing VM:
# virsh list –all
# virsh distroy machineName – is stopping immediately.
Start:
# virsh start machineName
All VM have configuration files.
the files are into:
# cd /etc/libvirt
Those are the configurations for libvirtd
QEMU is an emulator which is old which is used in KVM environment.
cd /etc/libvirt/qemu
Those are configuration files for VM.
# vi vmName.xml
The best way to edit the configuration is by using virsh:
# virsh edit vmName
In this file are details about VM and also the disk image file which is not the best as performance but easiest to implement.
Check the network of virtual VM:
# ip link show

Start virt-manager:
# virt-manager

Packages:
# yum install -y kvm libvirt virt-manager qemu-kvm

# yum repolist
The result is not OK.
Repository are on internet or can be a directory on server Example: /repo
# cd /etc/yum.repos.d/
Create a file:
# vi myrepo.repo
This is important that the file name is .repo.
3 things are very important:
Label:
[myrepo]
name=myrepo
baseurl=file:///repo
This is using an URI which can be file:// if is local or http:// or ftp://. After that is the path to repository. If is local it starts with /. There will be 3 slashes: /// !!!!!!!!!!
gpgcheck=0
This will switch off the file integrity.
For test is ok because it is hard to setup other steps.
Check it:
# yum repolist
Check the repository list:
# yum search ftp
# which cronyd
This is the process used to manage cron service.
The name of the process is /sbin/chronyd
Find from rpm:
# rpm -gf /sbin/cronyd
I see that the name of the RPM is chrony
Find all what is in the package:
# rpm ql chrony
Before installing scripts check the packages. If the packages are downloaded, check it like this:
# rpm -ql packageName
# rpm -qpl packageName
Check the scripts:
# rpm -qp –scripts packageName
Install a local package which is not in repository:
# yum localinstall packageName
Useful command:
# repoquery – is checking the packages while are in repository:
# repoquery -ql yp-tools

Install manually a repository:
wget ftp://server.example.com/repository
Extract
# createrepo /downloads
# repoquery – request information.

for see the process and child information use:
# ps fax
memory:
# free -m
(-m – megabytes)
# killall dd (terminate the processes with dd name)
# nice –help
nice [option] [command]
# nice -n 10 httpd
renice – for running processes
# renice -n -10 PID

# nmtui
These connections are managed by SystemManager
# systemctl restart NetworkManager
# systemctl status NetworkManager
check the connection information:
# ip a
Temporary base:
# ip route show
# ip route add 10.0.1.0/24 via 192.168.4.44
This route say to computer the next IP hop from routing steps.
Make the route permanent by edit the file:
# vi /etc/sysconfig/network-scripts/ifcfg-ens33
GATEWAY=192.168.3.4
After doing changes use the restart:
# nscli con down ens33; nmcli con up ens33

Troubleshooting:
# hostname
# ping example.com
# traceroute example.com
# dig example.com
# nmap example.com
# netstat -tulpen

first getfacl
# getfacl
Access control list will copy the permissions to ACL and will lose permissions from files/directory.
# setfacl -R -m g:sales:rx /directory
Apply default for future items
# setfacl -m d:g:sales:rx /directory
check facl for new directory:
# getfacl
Get the man page for example:
# man setfacl