LinuxLearning

Introduction
Configure SFTP for Web Server
Xrdp port and Clip copy issue
Scanning after adding new harddisk or increasing size
Performance and System Utilization Report
Add and remove the disk
Fix the sudoers syntax error without root password
Remove floppy disk
Assigning ip address
Reset the root password on centos7
Generate CSR using openssl
different ways to test a TCP port without telnet

What is this?

I have started as a habit to document anything that I will do on Linux. It is not only help my documentation but also a reference for me and others.

Configure SFTP for Web Server

This configuration for configuring sftp users to uploade the files from computers to apached document root directory such as /var/www/html

Create a sftp user:
useradd webtester
passwd webtester

Restrict user to the document root
edit vi /etc/ssh/sshd_config put following content:

Subsystem sftp internal-sftp
Match User webtester
    ChrootDirectory /var/www/
    ForceCommand internal-sftp -u 0022
    X11Forwarding no
    AllowTcpForwarding no
    PasswordAuthentication yes ```

Restart the sshd service:
service sshd restart
Chaange the owner and gropu of html directory
chown webtester:webtester /var/www/html

That's is all. It is easy right?
you can test it uploading indext.html from your desktop any linux box using winscp.

Note: if you want allow multiple users to upload then you can create a group called sftpuser and add all the users to that group. you can change Match User webtester to Match Group sftpusers and chown root:sftpuser /var/www/html and chmod 775 /var/www/html

Xrdp and session getting terminated once you select or copy anything

I recently faced an issue that user unable to take rdp session on Linux machine. The main issue I found that port 3389 wasn't listening

Edit xrdp.ini
```
port: 3389
```
service xrdp restart
work around for copy paste issue.
Edit .bashrc of user that facing the issue and add following:

/usr/bin/vncconfig -get SendPrimary 2>/dev/null
if [ $? -eq 0 ];
then
        /usr/bin/vncconfig -set SendCutText=0
        /usr/bin/vncconfig -set SendPrimary=0
fi

source /home/<user_name>/.bashrc
service xrdp restart

Hopefully these steps will fix the issue.

Scanning after adding new harddisk or increasing size

Adding new disk: you can run the below command to discover the newly added disk on host
echo "- - -" >> /sys/class/scsi_host/host_$i/scan
where $i is the host number

Example:
```
  echo "- - -" >> /sys/class/scsi_host/host0/scan   
  echo "- - -" >> /sys/class/scsi_host/host1/scan
  echo "- - -" >> /sys/class/scsi_host/host2/scan
```
Note: If the added disk doest show up on the host after rescan, Please readd the disk with different scsi id.
Adding more space to existing disk: If the added space doesn't show up on the host then you run the following command:
echo 1 > /sys/class/scsi_device/0\:0\:0\:0/device/rescan
echo 1 > /sys/class/scsi_device/0\:0\:1\:0/device/rescan

You can run the above command based on the disk ID. IF you added space then fist disk then run on 0:0:0:0
Extending the mounted disk without Partition:
You can create physical volume directly from disk without partitioning it such as:
pvcreate /dev/sdd

once you have creaed the pv then you can create VolumeGroup(VG) adn LVM.

Whenever you want to extend the disk which is used to create PV without partition, you need to run following command after increasing the size and running the disk scan.
pvresize /dev/sdd
Automatically it increases the VG as well that is created from this disk.

Performance and System Utilization Report

dstat is a excellent pefomance monitoring tool to provide the combined report that is provided by indivual command as vmstate, iostate, netstat, mpstate etc
- Installation
  yum install dstat
  man dstat # detail information and options available
- Examples:
  dstat
  It gives following output:
  - CPU stats:
    cpu usage by a user (usr) processes, system (sys) processes, as well as the number of idle (idl) and waiting (wai) processes, hard interrupt (hiq) and soft interrupt (siq).
  - Disk stats:
    total number of read (read) and write (writ) operations on disks.
  - Network stats:
    total amount of bytes received (recv) and sent (send) on network interfaces.
  - Paging stats:
    number of times information is copied into (in) and moved out (out) of memory.
  - System stats:
    number of interrupts (int) and context switches (csw)
    dstat -c #CPU stats dstat -d #Disk read/write
Adding new disk: dstat -m #memory stats
dstat -n # network stats
dstat -g# paging stats
dstat -y # system stats
dstat -p # running process
dstat -r # read and write stats
dstat -s # swap details
dstat -tcdm --output report.csv # it stores the time, cpu, disk and memory in report.csv file
systate

Add and remove the disk

Adding new disk:
Let say that you want to add a disk with 100GB, create a partition,create lvm with that partion and mount on /data directory.
once you attached the disk to vm from Vcenter/Vcloud, the disk mayn't be visible on OS
you can run the below command to discover the newly added disk on host echo "- - -" >> /sys/class/scsi_host/host_$i/scan where $i is the host number

Example:
```
  echo "- - -" >> /sys/class/scsi_host/host0/scan
  echo "- - -" >> /sys/class/scsi_host/host1/scan
  echo "- - -" >> /sys/class/scsi_host/host2/scan
```
Note: If the added disk doest show up on the host after rescan, Please readd the disk with different scsi id.
You can verify the disk by running fdisk -l command, You will see a disk such as /dev/sdb 100GB
- Partition the disk:
  The partition can be created by running fdisk /dev/sdb and provide following: # please note that /dev/sdb is the device name
  n (new),
  p (primary),
  enter (default first block),
  enter (default last block),
  enter (default block size),
  t (providing filetype),
  enter (default takes the 1st partition),
  8e (code for Linux LVM),
  w (write changes),
  Run partprobe -s to discover the newly created partioned that is #/dev/sdb1 verify the partition by running fdisk -l
- Create physical volume(PV) from newly created partition
  pvcreate /dev/sdb1 and verify by pvs
- Create Volume Group(VG) vgcreate vg_data /dev/sdb1 vg_data is the name of the volume group and verify by running vgs
- Create Logical Volume Group(lvm)
  lvmcreate -n lv_data -l+100%FREE vg_data # This creates lv_data lvm with all 100GB space and verify by running lvs or lvdisplay
- We need to create the filesystem such xfs mkfs.xfs /dev/vg_data/lv_data
- Create a directory mkdir /data
- Add the entry in /etc/fstab file vi /etc/fstab
  /dev/mapper/vg_data-data /data xfs defaults 0 0
- Finally mount it mount -a
- verify using df -hT # you can see the /data partition with 100GB
Removing disk:
After creating the /data partition, you have reliased that you need to devide the 100GB to /data and /home. The main problem is here that /data and /home are from different volume group(vg) that vg_data and vg_root. The only solution we have to remove the partition and disk and create 2 partition of each 50GB, creat pvs with those partion for differrent voulme group.
- Please note these steps will delte your data. so please backup and careful. Need to perform following steps:
  - unmount /data If it fails due to device busy then you have find the process using that /data using lsof | grep "/data" and kill that process
  - Edit the fstab entry
    vi /etc/fstab #/dev/mapper/vg_data-data /data xfs defaults 0 0
  - lvremove /dev/mapper/vg_data-data # Remove lv_data lvm
  - vgremove vg_data # remove volume group vg_data
  - pvremove /dev/sdb1 # Remove physical volume(PV)
  - echo "- - -" > /sys/class/scsi_host/host0/scan # scan for change in fstab file
  - We are safe now to remove the disk from Vcenter/vcloud.
  - echo 1 > /sys/block/sdb/device/delete # To Mark device is delete.
  - echo "- - -" > /sys/class/scsi_host/host0/scan # scan for the changes and makes sure that disk removed completely from Memory.
  - Add the disk now from from Vcenter/vcloud and run the below command to discover the newly added disk on host.
    `` echo "- - -" >> /sys/class/scsi_host/host_$i/scan``` where $i is the host number
  Example:
```
echo "- - -" >> /sys/class/scsi_host/host0/scan
echo "- - -" >> /sys/class/scsi_host/host1/scan
echo "- - -" >> /sys/class/scsi_host/host2/scan
```
  Note: If the added disk doest show up on the host after rescan, Please readd the disk with different scsi id. You can verify the disk by running fdisk -l command, You will see a disk such as /dev/sdb 100GB
  - Partition the disk:
    The partition can be created by running fdisk /dev/sdb and provide following: # please note that /dev/sdb is the device name
    n (new),
    p (primary),
    enter (default first block),
    enter (+50GB),
    t (providing filetype),
    enter (default takes the 1st partition),
    8e (code for Linux LVM),
    w (write changes),
    Run partprobe -s to discover the newly created partioned that is #/dev/sdb1
    verify the partition by running fdisk -l and follow the steps to create pv, vg, lv , filesytem and mount as given the steps in adding hardisk section.
    Now we have to create another partion such as /dev/sb2 for extending the /home partion by 50GB.
  - Partition the disk:
    The partition can be created by running fdisk /dev/sdb and provide following: # please note that /dev/sdb is the device name
    n (new),
    p (primary),
    enter (default first block),
    enter (defalut last sector),
    t (providing filetype),
    enter (default takes the 1st partition),
    8e (code for Linux LVM), w (write changes),
    Run partprobe -s to discover the newly created partioned that is #/dev/sdb2
  - Extend the /home partition
    Let assume that the /home partition has created using vg_root volume group and lv_home logical volume
  - Create physical volume(PV) from newly created partition /dev/sdb2
    pvcreate /dev/sdb2 and verify by pvs
  - Extend vg_data volume group vgextedn vg_data /dev/sdb2 vg_data is the name of the volume group and verify by running vgs. You will see 50GB free
  - Extend vg_root Logical Volume Group(lvm)
    lvextend -l+100%FREE /dev/mapper/vg_data-lv_root
  - Grow the xfs filesystem
    xfs_growfs /dev/mapper/vg_data-lv_root
  - Extend the ext4 filesystem
    resize2fs /dev/mapper/vg_data-lv_root
  - verify by running df -hT
  SudoFix
  - Edit the /etc/sudoers file suing pkexec visudo it will prompt for which user you want to authenticate with.
  Remove floppy disk
  - rmmod floppy
  - echo "blacklist floppy" | tee /etc/modprobe.d/floppy-blacklist.conf
  - update-initramfs -u
Assigning ip address

We can assign the IP addresses using the nmcli command
*nmcli con show # It lists the connection(ethernet interfaces)
- nmcli con add con-name eth1 type ethernet ifname eth1 # add new connection of type ethernet
- nmcli con mod eth1 ipv4.addresses 192.168.10.100/24 # Assign the ip address to the newly interface
- nmcli con mod eth1 ipv4.method manual autoconnect yes # making change permanent
- nmcli con mod enp0s3 ipv4.gateway 192.168.1.1
- nmcli con mod enp0s3 ipv4.dns "8.8.8.8"
- nmcli con up eth1
- nmcli con mod eth1 ipv6.addresses fbbd:fe2a:able::c0a8:64 # Ipv6
- nmcli con mod eth1 ipv6.method manual
- nmcli con up eth1
- ip add add 192.168.10.100/24 dev ens160 # Using IP command
- ip link set dev ens160 up # activate the interface
- ip route add default via 192.168.1.1dev ens160 # add default route
Reset the root password on centos7
- select the rescue mode
- press "e"
- find the kernel line (starts with "linux16")
- change ro to rw and add init=/sysroot/bin/sh
- press ctrl+x
- chroot /sysroot/
- passwd root
- touch /.autorelabel
- exit
- rebooot
Generate CSR using openssl
```
 # Genrate csr using below command:  
   * openssl req -new -newkey rsa:2048 -nodes -keyout example.com.key -out exmaple.com.csr  
  # Please replace #example.com with your domain name and provide following details 
  Country Name (2 letter code) [AU]:AE  
  State or Province Name (full name) [Some-State]:Dubai  
  Locality Name (eg, city) []:Dubai  
  Organization Name (eg, company) [Internet Widgits Pty Ltd]:Testing  
  Organizational Unit Name (eg, section) []:IT  
  Common Name (e.g. server FQDN or YOUR name) []:example.com  
  Email Address []:abc@example.com  
  
  # Verify the newly generated CSR using below command  
     * openssl req -text -noout -verify -in example.csr    
```
different ways to test a TCP port without telnet
```
 # BASH
   * cat < /dev/tcp/127.0.0.1/22  
    SSH-2.0-OpenSSH_5.3  
    ^C
   * cat < /dev/tcp/127.0.0.1/23  
     bash: connect: Connection refused  
     bash: /dev/tcp/127.0.0.1/23: Connection refused   
     
 # cURL  
  * curl -v telnet://127.0.0.1:22  
    About to connect() to 127.0.0.1 port 22 (#0)  
    Trying 127.0.0.1... connected
    Connected to 127.0.0.1 (127.0.0.1) port 22 (#0)
    SSH-2.0-OpenSSH_5.3
    ^C
  * curl -v telnet://127.0.0.1:23
    About to connect() to 127.0.0.1 port 23 (#0)
    Trying 127.0.0.1... Connection refused
    couldn't connect to host
    Closing connection #0
```

hussainaphroj/LinuxLearning

LinuxLearning

Table of contents

What is this?

Configure SFTP for Web Server

Xrdp and session getting terminated once you select or copy anything

Scanning after adding new harddisk or increasing size

Example:

Performance and System Utilization Report

Add and remove the disk

Example:

Example:

SudoFix

Remove floppy disk

Assigning ip address

Reset the root password on centos7

Generate CSR using openssl

different ways to test a TCP port without telnet