Some Computer Hints

Linux General

The grep -w command form matches whole words only. The -r option searches subdirectories. For example to find all the files under /etc that contain the current hostname:

$ grep -rwi $(hostname) /etc

To copy all files from /source directory to /dest directory use the following commands:

# cd /source
# find . -xdev | cpio -pduvlm /dest
# cd /source
# find . -type d -exec chmod --reference='{}' /dest/'{}' \;
# find . -type d -exec chown --reference='{}' /dest/'{}' \;

The shred command can be used to securely erase a file by overwriting it multiple times with random bit patterns before deleting it.

strace is the Linux equivalent of truss, i.e., a diagnostic and debugging tool for tracing system calls and signals. The simplest way of invoking it is:

# strace command

Adding an appropriate entry to /etc/logrotate.conf makes it possible to manage personal log files, as well as system-wide ones.

tac is the inverse of cat, listing a file backwards from its end. rev reverses each line of a file and outputs to stdout; this is not the same effect as tac, as it preserves the order of the lines, but flips each one around.

The pidof command identifies the process ID (PID) of a running process. For example,

$ pidof cron

will return the process ID of cron daemon.

dumpe2fs dumps to stdout very verbose filesystem information. For example, run

# /sbin/dumpe2fs /dev/hda1

Note that, dumpe2fs resides under the /sbin directory.

To display all kernel parameters execute

# /sbin/sysctl -a

To make kernel parameter changes (permanently) edit /etc/sysctl.conf file.

For hardware information use

# lspci -vv


# lsusb -tv

To see your ethernet interface speed use a command like

# mii-tool -v eth0

Important system information can be obtained from the “files” under /proc/ directory. For example enter

$ cat /proc/meminfo

for current memory usage information; or

$ cat /proc/swaps

for a list of swap devices. As another example, the file /proc/bus/usb/devices contains information about the USB ports on the system. For example, Spd=12 indicates USB 1.1 ports, while Spd=480 indicates USB 2.0 ports.

Disk information can be obtained with

# fdisk -l

To get hardware disk information try the commands:

# smartctl -a /dev/hda
# hdparm -iv /dev/hda

To check service status use

# service --status-all

To restart a service (for example, xinetd) enter

# service xinetd restart