TechBytes on Linux

This is a growing list of Linux commands which might come handy for the newbies of Linux.

1. Found out i had to set the date like this:
   # date -s 2007.04.08-22:46+0000

2. Mounting
    sudo mount -t cifs // < pingable_host_or_ip > / < win_share_name > /build -o user=,domain=,uid=string,gid=string

3. To install linux packages from internet (ubuntu only)
    apt-get install

4. To determine what ports the machine is currently listening on
    netstat -an | grep -i listen | less

5. Find in files in Linux
    find . | xargs grep 'string' -sl

6. To become superuser/root
    sudo -i

7. To find a running process using name

ps -aef | grep "searchstring"

8. Alt + F2 opens run window in RHEL

9. To access windows share from linux
smb:///d$

10. To know the last reboot date & time
$ last reboot | head -1

11. To install RPM packages in RHEL
rpm -ivh

12. To un-install RPM package in RHEL
rpm -e

13. To display Linux Kernel version
uname --all

14. To list out the Linux partitions
cat /proc/partitions

15. To list of all writable storage devices in Linux
fdisk -l

16. Installing software from sources in Linux
http://www.tuxfiles.org/linuxhelp/softinstall.html

17. The -T option in the df command displays the file system type.
df -T

18. Open current directory from within the terminal
xdg-open .


18. Find out details about the CPU such as speed, type, no of cores etc
cat /proc/cpuinfo

19. Find out details about memory installed
cat /proc/meminfo
vmstat

20. To list out installed rpms
rpm -qa

21. To Disable firewall on RHEL 7.2
systemctl stop firewalld
systemctl status firewalld


22. Find out the Linux OS/Operating system version
a] /etc/*-release file.
b] lsb_release command.
c] /proc/version file.

23. Try this to reload your current shell

source ~/.profile

24. The following Linux commands can be used to search files by name.find /path -name *.txt
find /path -type f -name test.txt
find /path -name failed*.* -type f
find /path -type f -not -name “*.html”
find / -name “file.txt” -size +4M
find /dev/ -type b -name “sda*”

25. Proxy configuration on Ubuntu Linux

• apt-get, aptitude, etc. will not obey the environment variables when used normally with sudo. So separately configure them; create a file called 95proxies in /etc/apt/apt.conf.d/, and include the following:

  Acquire::http::proxy "http://myproxy.server.com:8080/";
  Acquire::ftp::proxy "ftp://myproxy.server.com:8080/";
  Acquire::https::proxy "https://myproxy.server.com:8080/";

 

26.  Scanning scsi disks in RHEL

1.Finding the existing disk from fdisk.

[root@mylinz1 ~]# fdisk -l |egrep '^Disk' |egrep -v 'dm-'
Disk /dev/sda: 21.5 GB, 21474836480 bytes

2.Find out how many SCSI controller configured.

[root@mylinz1 ~]# ls /sys/class/scsi_host/host
host0 host1 host2

In this case,you need to scan host0,host1 & host2.

3.Scan the SCSI disks using below command.

[root@mylinz1 ~]# echo "- - -" > /sys/class/scsi_host/host0/scan
[root@mylinz1 ~]# echo "- - -" > /sys/class/scsi_host/host1/scan
[root@mylinz1 ~]# echo "- - -" > /sys/class/scsi_host/host2/scan

4.Verify if the new disks are visible or not.

[root@mylinz1 ~]# fdisk -l |egrep '^Disk' |egrep -v 'dm-'
Disk /dev/sda: 21.5 GB, 21474836480 bytes
Disk /dev/sdb: 1073 MB, 1073741824 bytes
Disk /dev/sdc: 1073 MB, 1073741824 bytes

From Redhat Linux 5.4 onwards, redhat introduced “/usr/bin/rescan-scsi-bus.sh” script to scan all the SCSI bus and update the SCSI layer to reflect new devices.

Install it using yum -y install sg3_utils command.

But most of the time,script will not be able to scan new disks and you need go with echo command.

Useful link on how to configure iSCSI volumes

https://www.cyberciti.biz/tips/rhel-centos-fedora-linux-iscsi-howto.html 

-->