Useful CentOS 7.n Commands

If you administer CentOS Linux systems, the following commands would be useful.

Display current CentOS version : cat /etc/centos-release
Display current Linux kernel version : uname -mrs
Display shell environment variables and their values : env
Display list of commands previously run : history
How long has the system been up? : uptime -p or uptime -s for the last datetime the system was rebooted
Default systemd "target" (formerly "runlevel") : systemctl get-default
Current "target" : who -r
List CPUs : lscpu
Memory utilization (in MB) : free -m or cat /proc/meminfo for more detailed information
List BLOCK devices (sd=scsi device) : lsblk
Display disk storage usage : df -hT
List devices attached to the PCI bus : lspci -vv
List USB devices : lsusb -v
List loaded kernel device drivers (modules) : lsmod
Boot parameters (boot images are in /boot) : cat /proc/cmdline
Determine boot time (and startup time of various services) : systemd-analyze blame, then q to exit.
List configured services : ls -alH /usr/lib/systemd/system Also check ls -alH /etc/systemd/system
Get details of the sshd service : cat /lib/systemd/system/ssh.service
Point top at a particular process : top -p [pid]
List available i/o schedulers for a storage device (sdc) : cat /sys/block/sdc/queue/scheduler

Display the contents of the kernel ring buffer : dmesg -wH or tail -f /var/log/dmesg

Display details of a disk : fdisk -l /dev/sdc
List available i/o schedulers for a storage device (sdc) : cat /sys/block/sdc/queue/scheduler
Change i/o scheduler at runtime : echo cfq > /sys/block/sdc/queue/scheduler
Create an ext4 filesystem : mkfs.ext4 -L DATA -v /dev/sdc1
Mount a filesystem : mount -o rw,noatime /dev/sdc1 /mnt/crx
Entry in /etc/fstab : Get UUID with blkid then UUID=fs6g5hj5675dsg-7g7d5778gd-877558g87g /mnt/crx ext4 defaults 0 2
Verify /etc/fstab entries before rebooting : mount -a
Verify the health of a filesystem : umount /mnt/crx then fsck /dev/sdc1
Get details of a filesystem : tune2fs -l /dev/sdc1 or dumpe2fs /dev/sdc1
Get details of inode utilization : df -i /dev/sdc1

Get permissions for a folder : stat -c %a /mnt/crx for output in octal, or stat -c %A /mnt/crx
Get details of a file : stat /tmp/1.pdf
Create a symbolic link in /usr/files to the file /usr/pdf/1.pdf : ln -s /usr/pdf/1.pdf /usr/files/linkto1.pdf
Find all PDF files : find / -type f -name '*.pdf'
Find all PDF files using an index : locate '*.pdf' Index settings are in /etc/updatedb.conf (note that the contents of /tmp are excluded from the index)

stat bin

List all installed packages : rpm -qa
Get details of an already installed package (nano-2.3.1-10.el7.x86_64) : rpm -qi nano
Get details of a package file : rpm -qpi package.rpm
List the dependencies of a package file : rpm -qpR package.rpm
Install a package : rpm -ivh package.rpm
Yum (Yellowdog Updater Modified)configuration : /etc/yum.conf
Configured repositories : ls -alH /etc/yum.repos.d