List of Useful Linux Commands
Here is a list of basic Linux commands:
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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