Note: Please do not put any classified information in a banner file since banner message is displayed before entering user/password credential during ssh/scp session. 1. Create the text file that should appear as the warning. For example /etc/sshbanner.txt: [root@server]# vi /etc/sshbanner.txt ############################################################################################################################################################### # # WARNING TO USERS OF THIS … [Read more...] about How To Create A SSH Banner in CentOS/RHEL Server
Linux
Error: Can’t open display: hostname:x.y when running xclock
The Problem Unable to launch xclock window using the below command for one particular normal user. xclock is fine with the root user. $ xclock Error: Can't open display: [hostname]:x.y The Solution Incorrect user level environment variables set under the file /home/[username]/.bash_profile. Follow the below steps to fix the issue. 1. Log in as a normal user. 2. Comment out all the user specific env variables under the file /home/[username]/.bash_profile. 3. Launch VNC … [Read more...] about Error: Can’t open display: hostname:x.y when running xclock
‘ulimit: max user processes: cannot modify limit:operation not permitted’ Shown When Login
The Problem When login as oracle user, the following message showed on the console. -bash: ulimit: max user processes: cannot modify limit:operation not permitted. The Solution ulimit option '-u' which means maximum number of user processes was set to a bigger one directly by adding the following line in the $HOME/.bash_profile. $ ulimit -u 4096 $ ulimit -u 4096 But originally the maximum number of user processes was set to 1024 in /etc/profile for oracle user. if [ $USER = … [Read more...] about ‘ulimit: max user processes: cannot modify limit:operation not permitted’ Shown When Login
“530 Non-anonymous sessions must use encryption” – while using curl
The Problem "Non-anonymous sessions must use encryption" occurs when running curl command as root user: # curl -v -k --ftp-ssl --ftp-pasv ftp://192.168.X.X:990/ --user hcpa:XXX * About to connect() to 192.168.X.X port 990 (#0) * Trying 192.168.X.X... connected * Connected to 192.168.X.X (192.168.X.X) port 990 (#0) < 220 FTP SERVER INFOVALMER. > USER hcpa < 530 Non-anonymous sessions must use encryption. * Access denied: 530 * Closing connection #0 curl: (67) Access denied: … [Read more...] about “530 Non-anonymous sessions must use encryption” – while using curl
How To Generate An CentOS/RHEL 6 UEFI Bootable ISO Image
1. Mount CentOS/RHEL 6.9 installation iso into /media/RHEL6.9; # mkdir /media/RHEL6.9 # mount -o ro /dev/cdrom /media/RHEL6.9 2. Create a new folder /opt/make_iso; # mkdir /opt/make_iso 3. Copy all files of CentOS/RHEL 6.9 installation iso to /opt/make_iso; # tar cf - /media/RHEL6.9 | ( cd /opt/make_iso/; tar xpvf - ) 4. Copy uefi kickstart config file to the root directory of iso image: # cp uefi_ks.cfg /opt/make_iso/ks.cfg 5. Copy efiboot.img to the root directory of iso … [Read more...] about How To Generate An CentOS/RHEL 6 UEFI Bootable ISO Image
Shopt: Not Found [No Such File Or Directory]
The Problem When a user logs in to the terminal using a user with the korn shell (ksh) the following messages occur: Shopt: Not Found [No Such File Or Directory] The Solution The following line was added on /etc/profile: shopt -s histappend Note: /etc/profile is a configuration file which sets the global environment for all users. As per man page of shopt: # man shopt shopt is part of BASH_BUILTINS -s Display readline key sequences bound to macros and the strings they … [Read more...] about Shopt: Not Found [No Such File Or Directory]
How to Update the hostname in Shell Prompt Once it is Changed in the Linux OS
Question: In this case, the hostname(geeklab) has already been updated in /etc/sysconfig/network and /etc/hosts file, but still needs to be updated in the shell prompt. For example, to change the old shell prompt as below: From : [root@geek ~]# To : [root@geeklab ~]# OS: CentOS/RHEL 6 and 7 Changing the Shell Prompt On the fly The shell prompt is controlled using the PS environment variables. Here is the list of commonly used PS environment variables and their function. PS1 - The … [Read more...] about How to Update the hostname in Shell Prompt Once it is Changed in the Linux OS
How to analyze basic system performance using – vmstat, sar, iostat and mpstat
In this post, a number of basic profiling tools that are included in most Linux systems by default will be discussed. The tools introduced in this post, vmstat, sar, iostat, and mpstat, are relatively simple but provide basic data which can be very useful when analyzing a system's performance. For most examples we will be using a CentOS 8 machine. vmstat: Virtual memory statistics One of the most useful tools when troubleshooting memory-related performance issues is vmstat. The vmstat … [Read more...] about How to analyze basic system performance using – vmstat, sar, iostat and mpstat
Difference between the Java heap and native C heap
A Java process basically consists of two different heap spaces. The Java heap (new, old and perm space) And the so called native C heap. The above is often confusing when it comes to OutOfMemory errors and allocation failures. In particular in 32-bit mode where the overall process space is limited to 4gb or even 2gb depending on the OS. As mentioned before, the total process size in 32-bit mode is limited to 4gb maximum. Java heap and C heap combined, along with other spaces, e.g. … [Read more...] about Difference between the Java heap and native C heap
Rpm: Error While Loading Shared Libraries: Libz.so.1: Cannot Open Shared Object File: No Such File
The Problem When executing rpm command, the following error is seen: rpm: error while loading shared libraries: libz.so.1: cannot open shared object file: No such file The zlib shard libraries are missing: # ls -l /lib64/libz.so* ls: /lib64/libz.so*: No such file or directory # ls -l /lib/libz.so* ls: /lib/libz.so*: No such file or directory The Solution The zlib was broken, normally zlib contains the following files. On x86_64 platform: # rpm -ql … [Read more...] about Rpm: Error While Loading Shared Libraries: Libz.so.1: Cannot Open Shared Object File: No Such File