Linux Commands frequently used
Linux Commands frequently used
Linux is a powerful and versatile operating system, and the command line is one of its most powerful features. The command line allows you to execute programs, manipulate files and edit text, all without using a graphical interface.
Learning even a few basic Linux commands can greatly increase your productivity, and help you automate repetitive tasks. In this article, we’ll introduce some of the most important Linux commands, with examples of how to use them.
SYSINFO
| Server Release Info | cat /etc/redhat_release |
| lsb_release | |
| Server Type | dmidecode |
| Hardwareinfo | lspci |
| lsusb | |
| lshal | |
| Note: hal = hardware abstraction layer | |
| Operating system | uname -a |
| Memory | cat /proc/meminfo |
| free -m | |
| cat /proc/slabinfo | |
| CPU (Type,number,etc) | cat /proc/cpuinfo (detailed) |
| Disk drives | fsdisk -l |
| sfdisk -l (advanced server) | |
| partprobe -s <device> | |
| Kernel File and associated directories | /boot/initrd.????.img |
| /boot/vmlinuz | |
| kernel 32 or 64 | uname -a |
| uname -m | |
| getconf -a | grep -i ‘long_bit’ | |
| Display Firmware | boot into the BIOS (normally F2 or F12) |
| Display IRQ, IO ports and DMA | /proc/interrupts |
| /proc/ioports | |
| /proc/dma | |
| GUI admin tool | linuxconf |
MEMORY AND SWAP
| MEMORY | cat /proc/meminfo (detailed) |
| Page size (memory) | /usr/bin/getconf -a | egrep -i ‘pagesize|page_size’ |
| Display Swap | cat /proc/swaps (detailed) |
| swapon -s | |
| Adding swap | device: |
| create partition with fdisk (type 82) | |
| file (create 50MB swap file): | |
| dd if=/dev/zero of=/var/swapfile | |
| bs=1024 count=50000 | |
| mkswap <device>|<file> | |
| swapon <device>|<file> | |
| update /etc/fstab | |
| removing swap | swapoff <device>|<file> |
| Remove device or file as normal |
DISKS, FILESYSTEMS AND DEVICES
| Disk drivers | fsdisk -l |
| sfdisk -l (advanced server) | |
| partprobe -s <device> | |
| Disk serial number, Type etc., | hdparm -i /dev/hda |
| hdparm -i /dev/hda (detailed) | |
| hdparm -Tt /dev/hda (speed test) | |
| sdparm -i /dev/sdb | |
| cat /proc/ide/ide0/hda/model | |
| cat /proc/scsi/scsi | |
| Disk Disk Partitions | fdisk -l |
| sfdisk -l (advanced server) | |
| cat /proc/partitions (very high level) | |
| cat /etc/fstab | |
| List raw partitions | ##old way |
| /etc/sysconfig/rawdevices | |
| service rawdevices start | |
| chkconfig rawdevices start | |
| ##New way, Edit below file | |
| /etc/udev/rules.d/60-raw.rules | |
| udevinfo -d or udevadm | |
| ##Display raw partitions | |
| raw -qa | |
| Filesystem commands | df -k |
| df -h | |
| Filesystem (create/remove) | mkfs -t ext 3 /dev/sdb1 |
| Tune file system | tune2fs |
| tune2fs -l /dev/sda1 | |
| Force fsck | touch /forcefsck |
| shutdown -Fr now | |
| tune2fs -l /dev/sdb<?> | grep -i ‘filesystem state’ | |
| backup filesystem | dump/restore |
| tar | |
| dd | |
| cpio | |
| Display the boot device | cat /boot/grub/grub.conf |
| cat /etc/lilo.conf | |
| grub = grand unified boot loader | |
| lilo= linux loader | |
| setting the boot device | /boot/grub/grub.comf |
| /etc/lilo.conf | |
| Creating boot device (MBR) | grub-install <raw-device> |
| lilo -v | |
| Fromat floppy drive | floppy –probe (use device obtained below) |
| floppy — createrc > /etc/fd0 | |
| floppy –format /dev/fd0 | |
| mkfs /dev/fd0 | |
| Mount/Unmount floppy | mount /dev/fd0/mnt/floppy |
| unmount /mnt/floppy | |
| Mount/Unmount CDROM | mount -rt iso9660 /dev/cdrom/mnt/cdrom |
| umount /mnt/cdrom | |
| eject cdrom | |
| Create boot disk or recovery tape | mkboot ‘uname -r’ (boot dsikette) |
| boot cdrom/diskette (single user) | using the grub window append the word single to the kernel line |
| boot into maintenance mode | f10 or f12 |
| Device Paths | floppy: |
| /dev/fd0 | |
| disk: | |
| /dev/hda or/dev/sda | |
| /dev/hdb or /dev/sdb | |
| tape: | |
| cdrom: | |
| /dev/hda (depends on number of IDE disks) | |
| update /dev directory | /dev/MAKEDEV <device> |
| remove or change a device | n/a |
| List device drivers | cat /proc/devices |
NETWORKING
| Basic network information (hostname, ip address) | /etc/sysconfig/networks |
| /etc/sysconfig/network-scripts/ifcfg-eth0 | |
| Displaying Network interfaces | ifconfig |
| system-config-network (GUI) | |
| Configure network interfaces | ifconfig |
| Starting and stopping a network interface | /sbin/ifup eth0 |
| /sbin/ifdown eth0 | |
| Setting NIC speed | mii-tool -F 100baseTx-Fd eth0 |
| ethtool -s eth1 speed 100 duplex full | |
| Change NIC parameters | mii-tool -v |
| ethtool eth1 | |
| ethtool -t eth0 online | |
| sysctl -a | grep net* | |
| Display Mac address | ifconfig |
| system-config-network (GUI) | |
| Displaying Network packets | tcpdump -i <interface> |
| ethereal (needs to be installed) | |
| Default router | edit /etc/sysconfig/network |
| add : GATEWAY=<IP address> | |
| display routing table | netstat -nr |
| route -n | |
| Test IPMP , BONDING | ifenslave -d bond0 eth1 (detach) |
| ifenslave -d bond0 eth1 (reattach) | |
| cat /proc/net/bonding/bond0 | |
| change the hostname | /etc/sysconfig/network |
| /etc/hosts | |
| sysctl -a | grep hostname | |
| setup DNS | /etc/resove.conf |
| Name service switch file (DNS client_ | /etc/nsswitch.conf |
| /etc/host.conf | |
| /etc/resolve.conf | |
| flush DNS cache | ## if installed |
| service nscd restart | |
| Domain name | /etc/sysconfig/network (hostname option) |
| /etc/resolv.conf | |
| Obtain IP address routing | ip route get <IP address> |
| traceroute | |
| Find services on the network | Boot (jumpstart) servers: |
| rpcinfo -b bootparam 1 | |
| NFS server: | |
| rpcinfo -b mounted 1 | |
| NIS server/slaves: | |
| rpcinfo -u <yp servers> ypserv |
CRASH DUMP
| Crash Dump | diskdump |
| netdump | |
| kdump (part of kexec rpm) | |
| /etc/kdump.conf (select where you want the dump to go) | |
| service kdump start | |
| chkconfig kdump on | |
| ## to crash the system | |
| echo “c” > /proc/sysrq-trigger | |
| crash (used to analyse crash dumps) |
PERFORMANCE MONITORING AND DIAGNOSTICS
| CPU | top |
| sar | |
| mpstat | |
| w | |
| uptime | |
| ps | |
| vmstat | |
| procinfo | |
| oprofile | |
| cat /proc/cpuinfo | |
| Memory | free |
| vmstat | |
| top | |
| procinfo | |
| slabtop | |
| sar | |
| cat /proc/meminfo | |
| Network I/O | ethtool |
| mii-tool | |
| netstat | |
| lsof | |
| tcpdump | |
| ip | |
| iptraf | |
| Disk I/O | sar -d |
| iostat | |
| vmstat | |
| lsof | |
| Application | strace -p <pid> |
| NFS | nfsstat |
KERNEL MODULES AND PARAMETERS
| Display loaded modules | cat /proc/modules (more detailed) |
| lsmodLocation: | |
| /lib/modules/’uname -r’ /kernel/drivers | |
| Config: | |
| /etc/modprobe.conf | |
| /etc/modprobe.d | |
| Load modules | modprobe <module> |
| insmod | |
| unloaded modules | modprobe -r <module> |
| rmmod | |
| Set kernel Parameters (tunig) | /etc/sysctl.conf (edit and update then reboot) |
| sysctl -p <filename>sysctl -w param=value | |
| No reboot (dynamically): | |
| echo “250 32000 100 28”> /proc/sys/kernel/sem | |
| echo”536870912″> /proc/sys/kernel/shmmax | |
| echo “4096”> /proc/sys/kernel/shmmni | |
| echo “2097152”> /proc/sys/kernel/shmall | |
| etc…………….. | |
| Display kernel parameters | sysctl -a |
| cat /etc/sysctl.conf | |
| cat /proc/sys/kernel/sem | |
| cat /proc/sys/kernel/shmmax | |
| etc…………….. | |
| Build kernel | cd /usr/src/linux-2.5 |
| edit Makefile (change EXTRAVERSION) | |
| make mrproper | |
| backup .config | |
| make xconfig | |
| make dep | |
| make bzImage | |
| make modules | |
| move nem kernel | |
| make modules_install | |
| change lilo/grub config file | |
| reboot | |
| Interprocess communication | ipcs -a |
SERVICES
| Display services | service –status all |
| start service | service nfs start |
| stop service | service nfs stop |
| reload service | service nfs reload |
| restart service | service nfs restart |
| service status | service nfs status |
| service dependencies | n/a |
| service logging, etc | n/a |
| change service start up | chkconfig –level 2345 nfs on |
| Add a new service | ## Create your stop/start |
| ##script in /etc/init.d | |
| chkconfig –add <script> |
PATCHING /SOFTWARE
| Adding patch | patch -p1 <patch> |
| zcat patch46.gz | patch -p1 | |
| Note : -p = # of patch stripping | |
| removing patch | patch -R -p1 <patch> |
| Display installed packages | rpm -qa (all packages) |
| rpm -qa (single package) | |
| rpm -qa (file belongs) | |
| rpm -qi <package> (very detailed) | |
| adding package | rpm -Uhv (updates/intalls if not already) |
| rpm -ivh (install) | |
| removing packages | rpm -e <package> |
| verify package | rpm -V <package> |
| List files ihn package | rpm -ql <package> |
| package directory | /var/lib/rpm |
| List libraries required for binary program | ldd <file> |
ACCOUNTS
| User creation | useradd |
| adduser (These may not work under some flavours) | |
| luseradd (These may not work under some flavours) | |
| To know create user exist or not | id name |
| su – username | |
| Remove all data of user | userdel -r name |
| To verify user password’s status | passwd -s username |
| To remove passwd | passwd -d username |
| To coustomize any flavours related to user account | usermod |
| To lock user account | usermod -s /sbin/nologin username |
| To revert it back | usermod -s /bin/bash username |
| To lock user passwd | usermod -L username |
| To unlock passwd | usermod -U username |
| Every user is identified with unique user id | |
| Types of users can be created | super user (root) UID range (0) |
| local user (user accounts created in every individual) | |
| domain user (user accounts in a centralised manner) | |
| system user ( Default users created while installing OS) | |
| Domian server (LDAP, NIS, IPA) | Domain environment configuration files |
| UID range for (local and domains) | |
| (1000 — 6,0000) | |
| (1-999) —- reserved for system users | |
| To create a group | groupadd user1 |
| Configuration file for group accounts information | /etc/group |
| To add a member into a secondary group | usermod -G security username |
| Removing user from a group | gpasswd -d username security |
| Adding user for a primary group | gpasswd -a username security |
| To change users primary group | usermod -g security username |
| To change username | usermod -l u1 username |
| To change UID for user | usermod -u 5000 username |
| To change group name | groupmod -n newname oldname |
| To change group id number | groupmod -g 3333 username |
| To change name of the user | mv /home/username /home/username2 |
| ls -l /home | |
| usermod -d /home/username2 username2 | |
| To recreate user’s home directory | mkdir /home/mani |
| chmod 700 /home/mani | |
| Important bash shell configurations | .bashrc —is used for shell configuration ,, we can store any kind of alias, userdefined functions, userdefined varialble and etc., |
| .bash_profile — It is used for login intialinzation which contains global built in variable functions | |
| /etc/skel — Default bash files are stored. | |
| cp /etc/skel/.bash* /home/username | |
| To change owner of the user | chown -R owner:groupname filename or directory |
| To create user home directory when it is deleted | mkhomedir_helper |
| chmod 700 /home/mani | |
| 7 fields in /etc/paswd | 1. username |
| 2.userpasswd |***| —/etc/shadow file | |
| 3.UID | |
| 4.GID (password file indicates users primary group) | |
| 5. ::—-> banner message, login prompt | |
| 6. home directory path for a username | |
| 7. shell for a user | |
| 3 fields in /etc/shadow | 1.username |
| 2. userpassswd (!!) it means it is locked | |
| userpasswd () it means empty passwd | |
| 3.account policy information | |
| 4 fields in /etc/group | 1. group name |
| 2. group passwords—-> passwd file will stored in /etc/gshadow | |
| 3.Id number | |
| 4. group number | |
| To display the default values | useradd -D |
| /etc/default/useradd | |
| /etc/login.defs ——> It conatins UID & GID range, It can change default home directory path | |
| Account Policy of a user | chage – I —-> value from last expires username |
| chage -m —-> (minimum no of days | |
| chage -w —> warning | |
| chage -E —-> account expiry | |
| chage -M —-> max no of days | |
| chage username | |
NFS
| Nfs Daemons | server:rpc.mountd,nfsd |
| client: rpc.statd, lockd | |
| NFS files | /etc/exports |
| /var/lib/nfs/etab | |
| /var/lib/nfs/xtab | |
| List nfs clients that have a remote mount | /var/lib/nfs/rmtab |
| Display nfs shares | showmount -e localhost |
| create nfs share | redhat-config-nfs (GUI) |
| /etc/exports (edit and share) | |
| /sbin/service nfs reload | |
| ## /etc/exports example | |
| /export *(rw,fsid=0,insecure,no_root_squash,sync) | |
| uncreate nfs share | /etc/exports (edit and remove share) |
| /sbin/service nfs reload | |
| start/change nfs daemons | /sbin/service nfs start |
| stop nfs daemons | /sbin/service nfs stop |
| nfs status | /sbin/service nfs status |
| nfs reload | /sbin/service nfs reload |
| nfs performance | nfsstat |
| nfs options | cat /var/lib/nfs/etab |
NTP
| Time daemons | ntpd |
| ntp setup | /etc/ntp.conf (edit with ntp servers) |
| dateconfig (GUI) | |
| chkconfig —list ntpd | |
| chkconfig — level 2345 ntpd on | |
| /sbin/service ntpd start | |
| ntp daemon options | /etc/sysconfig/ntpd |
| NTP trace commands | ntpq -p |
| ntptarce |
LOG FILES
| Messages | /var/log/messages |
| /var/log/syslog | |
| /var/log/mail.* | |
| /var/log/cron.log | |
| boot | /var/log/boot/dmesg |
| Error logging | logging |
SECURITY
| Checking the passwd file | pwck |
| Checking the group file | grpck |
| console login (allow/deny) | ## No reboot required |
| /etc/securetty |
MISC
| Startup | grub (GUI) |
| lilo(text based) | |
| shutdown | shutdown -h (halt) |
| shutdown -r (reeboot) | |
| shutdown -f (fast reboot no fsck) | |
| shutdown -F (force fsck) | |
| change run level | halt |
| init | |
| poweroff | |
| reboot | |
| shutdown | |
| telinit | |
| Init status | |
| 0 | 0- halt |
| 1 | 1-single user |
| 2 | 2- multiuser (no networking) |
| 3 | 3- multiuser (networking) |
| 4 | 4- unused |
| 5 | 5- GUI |
| 6 | 6- reboot |
| ##change default | |
| vi /etcinittab | |
| Startup options | single:- use grub to edit kernel line |
| emergency:- use grub to edit kernel line | |
| linux rescue:- use at the boot prompt | |
| single:-runlevel1, local fs mounted , no network | |
| emergency:-root fs read-only, no init files run | |
| rescue: use cd-rom/network, root mounted as /mnt/sysimage | |
| Startup scripts | /etc/init.d |
| /etc/rc0.d-/etc/rc6.d | |
| Boot prompt commands | F10 or F12 |
| Determine the run level | who -r |
| runlevel | |
| Obtain default run level | cat /etc/inittab |
| list locale | locale -a |
| start xwindows | startx (shorthand of below) |
| initx (lots of parms) | |
| Time Zone | /etc/sysconfig/clock |
| /usr/share/zoneinfo/zone.tab |
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