Category: Linux

Zero byte a File

/dev/null (zero out) a bunch of files at oncecd /var/logcat /dev/null | tee {boot.log,cron,dmesg,lastlog,messages,secure,vzctl.log,vznetcfg.log,wtmp} >boot.log>cron>dmesg>message

netmasks table

Decimal Binary CIDR Hex-------------------------------------------------------------------255.255.255.255 11111111.11111111.11111111.11111111 /32 ffffffff255.

sed Commands

sed one linersInsert character at beginning of lineComment all nfs entries in fstabsed -i '/nfs/s/^/#/' /etc/fstab Uncomment all nfs entries in fstabsed -i '/nfs/s/^#//g' /etc/fstab Su

nmap commands

Scan network for responsive IPsnmap -sS -O 10.199.42.0/23 | tee nmap.log Check if port is opennmap -P0 -p1521 oracle.com Scan UDPnmap -sU -p <port> <target>

tcpdump commands

Capture DHCP requestsPXE pxedhcp01 ~ # tcpdump -i eth1 \(port 67 or port 68\)tcpdump: verbose output suppressed, use -v or -vv for full protocol decodelistening on eth1, link-type EN10MB (Ethernet), c

tar / gzip commands

Here, we are sending the tar file to -, which stands for tar’s standard output. This is piped to gzip, which compresses the incoming tar file, and the result is saved in backup.tar.gz. The -c option t

Top CPU & Memory Processes

Display top 10 processes eating up CPUDisplay by processps -eo pcpu,pid,user,args | sort -k 1 -r | head -10 Display by userps -U apache -u apache u Display top 10 processes eating up memoryps axo %mem

/boot/grub/stage1 not read correctly

After pxe booting a server and installing linux from a cpio archive, grub failed to load using the grub-install command. The error presented was as follows: root@pxe:~# mkdir /targetroot@pxe:~# mount

How to Add Swap Space

How To Add Swap Space to a Linux SystemThere are two ways to go about adding swap space to a linux system. Use of a hard disk partition Create a swap file on an existing file system To view current

Enable auto logoff

Enabling automatic logoffSystems can be set to automatically logoff a user after a period of activity by setting some parameters: Linux/Solaris /etc/profile AIX /etc/security/.profile Parameter decl