hostnamectl
It shows the OS name and Linux kernel version & hostname.
lscpu
It gives the CPU related informations.
free / free -h
To show the RAM details
top / htop
It show the current running processes including cpu load average & Ram usage.
ls / ls -l / ls -lh / ls -lha
To list the files and folders in the current directory.
cd foldername / cd .. / cd /
To change the current directory & to go back & to go to root directory.
touch / nano filename
To create file and edit.
mkdir foldername
To create folder.
mv
To move files and directories from directory to directory. It also allows to rename files.
rm -rf foldername
To remove forlder including all sub folders & files.
rm / unlink
To remove or delete file.
df -h
Overall disk usage status of server.
du -h --max-depth=1 | sort -h
Disk usage of single location including sub folders. Short by size.
Count all files in a directory
ls . | wc -l
check max argument: getconf
ARG_MAX
Delete all files in a directory
find . -type f -exec rm -fv {} \;
find . -type f -name 'sess_*' -exec rm -fv {} \;
also can try
find . -maxdepth 1 -name sess_* -exec rm -r {} \;
find . -maxdepth 1 -name liton* -mtime +100 -exec rm -r {} \;