Skip to main content

sudo-su-vs-sudo-i-vs-sudo-bin-bash-when-does-it-matter-which-is-used

su - The command su is used to switch to another user (s witch u ser), but you can also switch to the root user by invoking the command with no parameter. su asks you for the password of the user to switch, after typing the password you switched to the user's environment.
sudo - sudo is meant to run a single command with root privileges. But unlike su it prompts you for the password of the current user. This user must be in the sudoers file (or a group that is in the sudoers file). By default, Ubuntu "remembers" your password for 15 minutes, so that you don't have to type your password every time.
bash - A text-interface to interact with the computer. It's important to understand the difference between login, non-login, interactive and non-interactive shells:
  • login shell: A login shell logs you into the system as a spiecified user, necessary for this is a username and password. When you hit ctrl+alt+F1 to login into a virtual terminal you get after successful login a login shell.
  • non-login shell: A shell that is executed without logging in, necessary for this is a currently logged-in user. When you open a graphic terminal in gnome it is a non-login shell.
  • interactive shell: A shell (login or non-login) where you can interactively type or interrupt commands. For example a gnome terminal.
  • non-interactive shell: A (sub)shell that is probably run from an automated process. You will see neither input nor output.
sudo su Calls sudo with the command su. Bash is called as interactive non-login shell. So bash only executes .bashrc. You can see that after switching to root you are still in the same directory:
user@host:~$ sudo su
root@host:/home/user#
sudo su - This time it is a login shell, so /etc/profile, .profile and .bashrc are executed and you will find yourself in root's home directory with root's environment.
sudo -i It is nearly the same as sudo su - The -i (simulate initial login) option runs the shell specified by the password database entry of the target user as a login shell. This means that login-specific resource files such as .profile, .bashrc or .login will be read and executed by the shell.
sudo /bin/bash This means that you call sudo with the command /bin/bash. /bin/bash is started as non-login shell so all the dot-files are not executed, but bash itself reads .bashrc of the calling user. Your environment stays the same. Your home will not be root's home. So you are root, but in the environment of the calling user.
sudo -s reads the $SHELL variable and executes the content. If $SHELL contains /bin/bash it invokes sudo /bin/bash (see above).
Check: To check if you are in a login shell or not (works only in bash because shopt is a builtin command):
shopt -q login_shell && echo 'Login shell' || echo 'No login shell'

Comments

Post a Comment

Popular posts from this blog

Interpreting the output of lspci

On Linux, the lspci command lists all PCI devices connected to a host (a computer). Modern computers and PCI devices communicate with each other via PCI Express buses instead of the older Conventional PCI and PCI-X buses since the former buses offer many advantages such as higher throughput rates, smaller physical footprint and native hot plugging functionality. The high performance of the PCI Express bus has also led it to take over the role of other buses such as AGP ; it is also expected that SATA buses too will be replaced by PCI Express buses in the future as solid-state drives become faster and therefore demand higher throughputs from the bus they are attached to (see this article for more on this topic). As a first step, open a terminal and run lspci without any flags (note: lspci may show more information if executed with root privileges): lspci   This is the output I get on my laptop: 00:00.0 Host bridge: Intel Corporation Haswell-ULT DRA...
Post a Comment
Read more

Boot process hangs at dracut: Switching root

Environment Red Hat Enterprise Linux 6 Issue When server is booting the boot process hangs at  dracut: Switching root , and never displays anything else. Raw device-mapper: ioctl: 4.33.1-ioctl (2015-8-18) initialised: xx-xxxx@redhat.com udev: starting version 147 dracut: Starting plymouth daemon dracut: rd_NO_DM: removing DM RAID activation dracut: rd_NO_MD: removing MD RAID activation scsi0 : ata_piix scsi1 : ata_piix ata1: PATA max MWDMA2 cmd 0x1f0 ctl 0x3f6 bmdma 0xc120 irq 14 ata2: PATA max MWDMA2 cmd 0x170 ctl 0x376 bmdma 0xc128 irq 15 Refined TSC clocksource calibration: 2599.999 MHz. virtio-pci 0000:00:03.0: PCI INT A -> Link[LNKC] -> GSI 11 (level, high) -> IRQ 11 virtio-pci 0000:00:05.0: PCI INT A -> Link[LNKA] -> GSI 10 (level, high) -> IRQ 10 virtio-pci 0000:00:07.0: PCI INT A -> Link[LNKC] -> GSI 11 (level, high) -> IRQ 11 virtio-pci 0000:00:08.0: PCI INT A -> Link[LNKD] -> GSI 11 (level, high) -> IRQ 11 input: ImExPS/2 G...
Post a Comment
Read more

How to Remove a Storage Device (LUN)

Before removing access to the storage device itself, it is advisable to back up data from the device first. Afterwards, flush I/O and remove all operating system references to the device. Stop all access to the device that has to be removed. Unmount the device. Remove the device from any md and LVM volume that is using it. If a multipath device is being removed, run  multipath -l  and take note of all the paths to the device. When this has been done, remove the multipath device: # multipath -f device   Use the following command to flush any outstanding I/O to all paths to the device: # blockdev –flushbufs device   Remove any reference to the device's path-based name, like  /dev/sd  or  /dev/disk/by-path  or the major:minor number, in applications, scripts, or utilities on the system. This is important to ensure that a different device, when added in the future, will not be mistaken for the current device. The fi...
Post a Comment
Read more