U

udevadm:- udev management tool

ul:- do underlining

ulimit:-

umask:-

umount:- unmount file systems

umount.nfs:- umount.nfs, umount.nfs4 - unmount a Network File System

umount.nfs4:- umount.nfs, umount.nfs4 - unmount a Network File System

unalias:-

uname:- print system information (Ex:- uname)

unexpand:- convert spaces to tabs

unicode_start:- put keyboard and console in unicode mode

unicode_stop:- revert keyboard and console from unicode mode

uniq:- report or omit repeated lines

unix_chkpwd:- Helper binary that verifies the password of the current user

unix_update:- Helper binary that updates the password of a given user

unlink:- call the unlink function to remove the specified file

unset:-

unshare:- run program with some namespaces unshared from parent

until:-

unxz:- xz is a general-purpose data compression tool with command line syntax similar to gzip(1) and bzip2(1).  The native file format is the .xz format,  but  the legacy .lzma format used by LZMA Utils and raw compressed streams with no container format headers are also supported.

unzip:- list, test and extract compressed files in a ZIP archive

unzipsfx:- self-extracting stub for prepending to ZIP archives

update-alternatives:- maintain symbolic links determining default commands

update-ca-trust:- manage consolidated and dynamic configuration of CA certificates and associated trust

updatedb:- update a database for mlocate

update-desktop-database:- Build cache database of MIME types handled by desktop files

update-gtk-immodules:- Update GTK+ immodule cache

update-mime-database:- a program to build the Shared MIME-Info database cache

update-pciids:- download new version of the PCI ID list

update-smart-drivedb:-

uptime:- Tell how long the system has been running. (Ex:- uptime)

urlgrabber:-

usb-devices:- print USB device details (Ex:- usb-devices)

usbhid-dump:- dump USB HID device report descriptors and streams

usb_modeswitch:- switch mode of "multi-state" USB devices

usb_modeswitch_dispatcher:- dispatcher not intended for direct invocation.

useradd:- create a new user or update default new user information

userdel:- delete a user account and related files

userformat:- A graphical tool to mount, unmount and format filesystems.

userhelper:- A helper interface to PAM.

userinfo:- A graphical equivilient to chfn.

usermod:- modify a user account

usermount:- A graphical tool to mount, unmount and format filesystems.

usernetctl:- allow a user to manipulate a network interface if permitted

userpasswd:- A graphical tool to allow users to change their passwords.

users:- print the user names of users currently logged in to the current host

usleep:- sleep some number of microseconds

usx2yloader:-

utmpdump:- dump UTMP and WTMP files in raw format

uuidgen:- create a new UUID value