Common administrative commands in Red Hat Enterprise Linux 5, 6, and 7
System basics
| Task | RHEL5 | RHEL6 | RHEL7 |
|---|---|---|---|
| View subscription information | /etc/sysconfig/rhn/systemid | /etc/sysconfig/rhn/systemid subscription-manager identity |
subscription-manager identity |
| Configure subscription | rhn_register subscription-manager 1 |
rhn_register rhnreg_ks subscription-manager |
subscription-manager2 rhn_register 3 |
| View RHEL version information | /etc/redhat-release | ||
| View system profile | sosreport dmidecode hwbrowser |
sosreport dmidecode lstopo lscpu |
|
Basic configuration
| Task | RHEL5 | RHEL6 | RHEL7 |
|---|---|---|---|
| Graphical configuration tools | system-config-* | gnome-control-center | |
| Text-based configuration tools | system-config-*-tui | ||
| Configure printer | system-config-printer | ||
| Configure network | system-config-network | nmcli nmtui nm-connection-editor |
|
| Configure system language | system-config-language | localectl | |
| Configure time and date | system-config-date date |
timedatectl date |
|
| Synchronize time and date | ntpdate /etc/ntp.conf |
timedatectl /etc/chrony.conf ntpdate |
|
| Configure keyboard | system-config-keyboard | localectl | |
| Configure SSH | /etc/ssh/ssh_config /etc/ssh/sshd_config ~/.ssh/config ssh-keygen |
||
Jobs and services
| Task | RHEL5 | RHEL6 | RHEL7 |
|---|---|---|---|
| List all services | chkconfig –list ls /etc/init.d/ |
systemctl -at service ls /etc/systemd/system/*.service ls /usr/lib/systemd/system/*.service |
|
| List running services | service –status-all | systemctl -t service –state=active | |
| Start/stop service | service name start service name stop |
systemctl start name.service systemctl stop name.service |
|
| Enable/disable service | chkconfig name on chkconfig name off |
systemctl enable name.service systemctl disable name.service |
|
| View service status | service name status | systemctl status name.service | |
| Check if service is enabled | chkconfig name –list | systemctl is-enabled name | |
| Create new service file or modify configuration | chkconfig –add | systemctl daemon-reload /etc/systemd/system/*.service |
|
| View run level/target | runlevel who -r |
systemctl get-default who -r |
|
| Change run level/target | /etc/inittab init run_level |
systemctl isolate name.target systemctl set-default |
|
| Configure logging | /etc/syslog.conf | /etc/rsyslog.conf | /etc/rsyslog.conf /etc/rsyslog.d/*.conf /var/log/journal systemd-journald.service |
| View logs | /var/log | /var/log journalctl |
|
| Configure system audit | add audit=1 to kernel cmdline auditctl /etc/audit/auditd.conf /etc/audit/audit.rules authconfig /etc/pam.d/system-auth pam_tty_audit kernel module |
||
| View audit output | aureport /var/log/faillog | ||
| Schedule/batch tasks | cron at batch |
||
| Find file by name | locate | ||
| Find file by characteristic | find | ||
| Create archive | tar cpio zip |
||
Kernel, boot, and hardware
| Task | RHEL5 | RHEL6 | RHEL7 |
|---|---|---|---|
| Single user/rescue mode | append 1 or s or init=/bin/bash to kernel cmdline | append rd.break or init=/bin/bash to kernel cmdline | |
| Shut down system | shutdown | ||
| Power off system | poweroff | poweroff systemctl poweroff |
|
| Halt system | halt | halt systemctl halt |
|
| Reboot system | reboot | reboot systemctl reboot |
|
| Configure default run level/target | /etc/inittab | systemctl set-default | |
| Configure GRUB bootloader | /boot/grub/grub.conf | /etc/default/grub grub2-mkconfig grub-set-default |
|
| Configure kernel module | modprobe | ||
| View hardware configured | hwbrowser | lshw (in EPEL) | |
| Configure hardware device | udev | ||
| View kernel parameters | sysctl -a cat /proc/cmdline |
||
| Load kernel module | modprobe | ||
| Remove kernel module | modprobe -r | ||
| View kernel version | rpm -q kernel uname -r |
||
Software management
| Task | RHEL5 | RHEL6 | RHEL7 |
|---|---|---|---|
| Install software | yum install yum groupinstall |
yum install yum group install |
|
| View software info | yum info yum groupinfo |
yum info yum group info |
|
| Update software | yum update | ||
| Upgrade software | yum upgrade | ||
| Configure software repository | subscription-manager repos /etc/yum.repos.d/*.repo |
||
| Find package owning file | rpm -qf filename yum provides filename-glob |
||
| View software version | rpm -q packagename | ||
| View installed software | rpm -qa yum list installed |
||
User management
| Task | RHEL5 | RHEL6 | RHEL7 |
|---|---|---|---|
| Graphical user management | system-config-users | ||
| Create user account | useradd | ||
| Delete user account | userdel | ||
| View/change user account details | usermod /etc/passwd vipw id |
||
| Create user group | groupadd | ||
| Delete user group | groupdel | ||
| Change group details | groupmod /etc/group |
||
| Change user password | passwd | ||
| Change user permissions | usermod visudo |
||
| Change group permissions | groupmod visudo |
||
| Change password policy | chage | ||
| View user sessions | w | ||
File systems, volumes, and disks
| Task | RHEL5 | RHEL6 | RHEL7 |
|---|---|---|---|
| Default file system | ext3 | ext4 | xfs |
| Create/modify disk partitions | fdisk parted |
fdisk gdisk parted ssm create |
|
| Format disk partition | mkfs.filesystem_type (ext4, xfs) mkswap |
mkfs.filesystem_type (ext4, xfs) mkswap ssm create |
|
| Defragment disk space | copy data to new file system fsck (look for ‘non-contiguous inodes’) |
copy data to new file system fsck (look for ‘non-contiguous inodes’) xfs_fsr |
|
| Mount storage | mount /etc/fstab |
mount /etc/fstab ssm mount |
|
| Mount and activate swap | /etc/fstab swapon -a |
||
| Configure static mounts | /etc/fstab | ||
| View free disk space | df | ||
| View logical volume info | lvdisplay lvs vgdisplay vgs pvdisplay pvs |
||
| Create physical volume | pvcreate | pvcreate ssm create (if backend is lvm) |
|
| Create volume group | vgcreate | vgcreate ssm create (if backend is lvm) |
|
| Create logical volume | lvcreate | lvcreate ssm create (if backend is lvm) |
|
| Enlarge volumes formatted with default file system | vgextend lvextend resize2fs |
vgextend lvextend xfs_growfs ssm resize |
|
| Shrink volumes formatted with default file system | resize2fs lvreduce vgreduce |
XFS cannot currently be shrunk; copy desired data to a smaller file system. | |
| Check/repair file system | fsck | fsck ssm check |
|
| View NFS share | showmount -e mount |
||
| Configure NFS share | /etc/exports service nfs reload |
/etc/exports systemctl reload nfs.service |
|
| Configure on-demand auto-mounts | /etc/auto.master.d/*.autofs /etc/auto.* |
||
| Change file permissions | chmod chown chgrp umask (future file creation) |
||
| Change file attributes | chattr | ||
| Change access control list | setfacl | ||
Networking
| Task | RHEL5 | RHEL6 | RHEL7 |
|---|---|---|---|
| Configure name resolution | /etc/hosts /etc/resolv.conf |
/etc/hosts /etc/resolv.conf nmcli con mod |
|
| Configure hostname | /etc/sysconfig/network | hostnamectl /etc/hostname nmtui |
|
| View network interface info | ip addr ifconfig brctl |
ip addr nmcli dev show teamdctl brctl bridge |
|
| Configure network interface | /etc/sysconfig/network-scripts/ifcfg-* | /etc/sysconfig/network-scripts/ifcfg-* nmcli con [add|mod|edit] nmtui nm-connection-editor |
|
| View routes | ip route | ||
| Configure routes | ip route add system-config-network /etc/sysconfig/route-iface |
ip route add nmcli nmtui nm-connection-editor /etc/sysconfig/route-iface |
|
| Configure firewall | iptables and ip6tables /etc/sysconfig/ip*tables |
iptables and ip6tables /etc/sysconfig/ip*tables system-config-firewall |
firewall-cmd firewall-config |
| View ports/sockets | ss lsof netstat |
ss lsof |
|
Security and identity
| Task | RHEL5 | RHEL6 | RHEL7 |
|---|---|---|---|
| Configure system security | /etc/selinux/config chcon restorecon semanage setsebool system-config-selinux |
||
| Report on system security | sealert | ||
| LDAP, SSSD, Kerberos | authconfig authconfig-tui authconfig-gtk |
||
| Network users | getent | ||
Resource management
| Task | RHEL5 | RHEL6 | RHEL7 |
|---|---|---|---|
| Trace system calls | strace | ||
| Trace library calls | ltrace | ||
| Change process priority | nice renice |
||
| Change process run location | taskset | ||
| Kill a process | kill pkill killall |
||
| View system usage | top ps sar iostat netstat vmstat mpstat numastat |
top ps sar iostat netstat ss vmstat mpstat numastat tuna |
top ps sar iostat ss vmstat mpstat numastat tuna |
| View disk usage | df | df iostat |
|
Simple questions
What is LD_LIBRARY_PATH?
- LD_LIBRARY_PATH is an environment variable. It is used for debugging a new library or a non-standard library. It is also used to identify what directories need to be searched. Path to search for directories needs to give.
- The variable can be set using setenv—LD_LIBRARY_PATH–$PATH.
- It is used to search for the shared objects / dynamic libraries by the operating system for extendable functionality at runtime.
How to check Memory stats and CPU stats as a Linux admin?
Using ‘free’ & ‘vmstat’ command, we can display the physical and virtual memory statistics, respectively. With the help of ‘sar’ command, we can see the CPU utilization & other stats.
What are the different modes of Network bonding in Linux?
Below is a list of modes used in Network Bonding :
- balance-rr or 0 – round-robin mode for fault tolerance and load balancing.
- active-backup or 1 – Sets active-backup mode for fault tolerance.
- balance-xor or 2 – Sets an XOR (exclusive-or) mode for fault tolerance and load balancing.
- broadcast or 3 – Sets a broadcast mode for fault tolerance. All transmissions are sent on all slave interfaces.
- 802.3ad or 4 – Sets an IEEE 802.3ad dynamic link aggregation mode. Creates aggregation groups that share the same speed & duplex settings.
- balance-tlb or 5 – Sets a Transmit Load Balancing (TLB) mode for fault tolerance & load balancing.
- balance-alb or 6 – Sets an Active Load Balancing (ALB) mode for fault tolerance & load balancing.
How to check and verify the status of the bond interface?
Using the command ‘cat /proc/net/bonding/bond0,’ we can check what mode is enabled and what LAN cards are used in this bond. In this example, we have one one bond interface. However, we can have multiple bond interfaces like bond1, bond2 and so on.
What is Puppet Server?
In computing, Puppet is an open-source software configuration management tool. It runs on many Unix-like systems as well as on Microsoft Windows, and includes its own declarative language to describe system configuration.
What is the name and path of the main system log?
By default, the main system log is ‘/var/log/messages’. This file contains all the messages and the script written by the user. By default, all scripts are saved in this file. This is the standard system log file, which contains messages from all system software, non-kernel boot issues, and messages that go to ‘dmesg’. dmesg is a system file that is written upon system boot.
What is YUM?
yum is the primary tool for getting, installing, deleting, querying, and managing Red Hat Enterprise Linux RPM software packages from official Red Hat software repositories, as well as other third-party repositories. yum is used in Red Hat Enterprise Linux versions 5 and later. Versions of Red Hat Enterprise Linux 4 and earlier used up2date.
What is the difference between ext2 and ext3 file systems?
- The ext3 file system is an enhanced version of the ext2 file system.
- The most important difference between Ext2 and Ext3 is that Ext3 supports journaling.
- After an unexpected power failure or system crash (also called an unclean system shutdown), each mounted ext2 file system on the machine must be checked for consistency by the e2fsck program. This is a time-consuming process and during this time, any data on the volumes is unreachable.
- The journaling provided by the ext3 file system means that this sort of file system check is no longer necessary after an unclean system shutdown. The only time a consistency check occurs using ext3 is in certain rare hardware failure cases, such as hard drive failures. The time to recover an ext3 file system after an unclean system shutdown does not depend on the size of the file system or the number of files. Rather, it depends on the size of the journal used to maintain consistency. The default journal size takes almost a second to recover, depending on the speed of the hardware.
Explain /proc filesystem?
/proc is a virtual file system that provides detailed information about Linux kernel, hardware and running processes. Files under /proc directory named as Virtual files.
Since /proc contains virtual files, it is called virtual file system. These virtual files have unique qualities. Most of them are listed as zero bytes in size.
Virtual files such as /proc/interrupts, /proc/meminfo, /proc/mounts, and /proc/partitions provide an up-to-the-moment glimpse of the system’s hardware. Others: /proc/filesystems file and the /proc/sys/ directory provide system configuration information and interfaces.
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