Root and Administrator Tasks: Process Management

UNIX root privileged accounts
If a process has a userid of 0, many restrictions such as permission checks from processes are not enforced (unless you are running SELinux.) These are generally called root processes; root processes can, tattoueba:

Root and Administrator Tasks: Process Management

Mount and unmount file systems -- however, that's not quite true on Linux machines; the mount(8) program is now being suid to root on some (many) distributions.

Root and Administrator Tasks: Process Management

If the keyword user is specified in a mount point defined in /etc/fstab, then many newer versions of the mount program will allow a user to mount or unmount that specific filesystem. (This is becoming a very smooth process in many distributions, and plugging in/removing a USB drive is now usually pleasant experience. While there is much flux here, some distributions are giving unique names such as the UUID name as part of the mount name; also, if you use LVM to create a volume group on a USB drive, then you can have a consistent logical name in /dev space.)

Root and Administrator Tasks: Process Management

Root processes can set a process's filesystem root to a subdirectory of a filesystem via chroot(2)
Create device files (/dev, mknod)
Set the system clock
Can access any local file

Root and Administrator Tasks: Process Management

Change file ownership
Raise resource limits (datasize, stacksize, coresize) -- no other userid than 0 can do so; other userids can only lower resources limits
Lower nice values (raising priority)

Root and Administrator Tasks: Process Management

Change system's hostname
Run halt, shutdown, telinit
Manage print subsystems

Root and Administrator Limitations: Process Management

Many other programs check to see if the current process is running under uid 0 (the code to check for this usually looks something like if geteuid() == 0) {...})

Root and Administrator Limitations: Process Management

What limitations and restrictions are there to such root processes?
UNIX suffers from ``userid 0 has all powers'', so root account (and its password(s)) is focus of security breakins.

Root and Administrator Limitations: Process Management

Mechanisms such as /etc/hosts.equiv should never be used to have root on one machine trust another. Instead, such trust, if needed, should be based on ssh using keys.
Should be careful that when acting as ``root'' that you know your $PATH. Beware of file paths in $PATH, especially the current working directory (``.'', aka as ``pwd'' or ``cwd'').

How to become ``root''? Generally, people use something along the way of `sudo`, `su`, or `login`

Ancient caveats: The login program still enforces criteria about using an ``allowed'' terminal (in /etc/ttytab (BSD), /etc/default/login (Solaris) or /etc/securetty (RedHat Linux).)

How to become root? `login`, `su`, `sudo`

Execute the su command
su = Substitute User

How to become root? `login`, `su`, `sudo`

su with minus flag (su - fc5) invokes a ``login'' session
Good idea to su - root. The advantages of a ``login'' shell:
Paths are those of root, not your current processes

How to become root? `login`, `su`, `sudo`

Set up items such as ``safe'' aliases for dangerous programs such as
rm → rm -i
cp → cp -i
mv → mv -i

sudo: pseudo su, or how to set up safer su

Ubuntu tries to make it de rigueur, others also
Allows a class of users to execute a set of commands with root privileges (the configuration is flexible enough to do lots more)

sudo: pseudo su, or how to set up safer su

Logs the use of the ``sudo'' command (but does not log the commands executed by the shells that are started by sudo !)
Does raise some vulnerabilities since it is yet-another setuid program (YASP?)

sudo: pseudo su, or how to set up safer su

# sudoers file.
#
# See the sudoers man page for the details on how to write a sudoers file.
#

# Host alias specification

# User alias specification

sudo: pseudo su, or how to set up safer su


# Cmnd alias specification

# Defaults specification

# User privilege specification
root	ALL=(ALL) ALL

# Uncomment to allow people in group wheel to run all commands
# %wheel	ALL=(ALL)	ALL

sudo: pseudo su, or how to set up safer su


# Same thing without a password
# %wheel	ALL=(ALL)	NOPASSWD: ALL

# Samples
# %users  ALL=/sbin/mount /cdrom,/sbin/umount /cdrom
# %users  localhost=/sbin/shutdown -h now

user1	monet=/usr/local/bin/suroot, /bin/su

System Load Average

``load average'' == average size of ready queue over sample period

Shows the 1, 5, and 15 minute load averages
Can see with w, uptime, or top

System Load Average

What's a reasonable load average? → depends on the machine and the type of jobs running
I am using a computer with quad-core and 4 gigabytes of memory to write these notes; it also has two processes crunching numbers and a load average over 2, but it's not loaded and is very responsive.

Idle Time

Percentage of time the system is idle
Can see with iostat -c 1, top, or vmstat 1
What do you want this number to be? (again, it depends on machine's raison d'être)

Idle Time

iostat -c 1
Linux 2.6.27.24-170.2.68.fc10.x86_64 (localhost.localdomain) 	06/11/2009

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          57.04    0.20    0.97    0.07    0.00   41.73

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          50.50    0.00    0.00    0.99    0.00   48.51

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          51.36    0.00    0.25    0.00    0.00   48.39

Process Monitoring: `ps`

ps comes from process status; LAH has comprehensive information
Shows a window into process table via the filesystem -- remember, ps these days generally is just walk through the /proc pseudo-filesystem

Process Monitoring: ps

Rich command options set; unfortunately, there are different options depending on whether the OS is BSD or System V based.

Process Manipulation:

As a system administrator, you can adjust the priority of a process with renice:

renice +19 PID    ##  lowest priority (nice)
renice -19 PID    ## highest priority (not nice)

Example `ps` output from long, long ago

USER       PID %CPU %MEM   SZ  RSS TT STAT START   TIME COMMAND
-----------------------------------------------------------------------
kuncick   7467 40.1 1.3   124  364 pc D <  09:32   0:15 find / -name foo
kuncick   7419 16.6 1.3   124  364 pc D N  09:28   0:11 find ... 
kuncick   7529 39.4 1.2   100  320 pc R    09:35   0:01 find / -name foo 
kuncick   7528 35.8 1.2   112  324 pc R    09:35   0:15 find / -name foo 
root         1  0.0 0.0    52    0 ?  IW   Dec 18  0:24 /sbin/init - 
root         2  0.0 0.0     0    0 ?  D    Dec 18  0:08 pagedaemon 
root        75  0.0 0.4    48  108 ?  S    Dec 18 12:09 in.routed 
bynum     7328  0.0 0.1    48   24 pb S    09:24   0:00 rlogin

Example `ps` output from the more recent past

F   UID   PID  PPID PRI  NI   VSZ  RSS WCHAN  STAT TTY        TIME COMMAND
--------------------------------------------------------------------------
5     0  1778     1  24   0  1528  512 -      S    ?          0:00 /usr/sbin/apmd -p
 10 -w 5 -W -P /etc/sysconfig/apm-scripts/apmscript
5     0  1866     1  15   0  2144  880 -      S    ?          0:00 xinetd -stayalive
 -pidfile /var/run/xinetd.pid
1    51  1902     1  15   0  5992 2284 -      S    ?          0:00 sendmail: Queue
 runner@00:01:00 for /var/spool/clientmqueue
1    49  1949     1  25   0  5296 4012 -      S    ?          0:00 /usr/bin/jserver

Example `ps` output from the more recent past

4   500  2089  2068  15   0 18364 8948 schedu S    ?          0:00 /usr/bin/gnome-session 
SSH_AGENT_PID=2140 HOSTNAME=sophie.cs.fsu.edu TERM=dumb SHELL=/bin/bash HISTSIZE=1000 
QTDIR=/usr/lib/qt-3.1 USER=langley LS_COLORS= SSH_AUTH_SOCK=/tmp/ssh-sQIL2089/agent.2089 
PATH=/usr/kerberos/bin:/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:/home/langley/bin 
MAIL=/var/spool/mail/langley PWD=/home/langley INPUTRC=/etc/inputrc XMODIFIERS=@im=none 
LANG=en_US.UTF-8 LAMHELPFILE=/etc/lam/lam-helpfile GDMSESSION=Default 
SSH_ASKPASS=/usr/libexec/openssh/gnome-ssh-askpass SHLVL=1 HOME=/home/langley 
LOGNAME=langley LESSOPEN=|/usr/bin/lesspipe.sh %s DISPLAY=:0 G_BROKEN_FILENAMES=1 
XAUTHORITY=/home/langley/.Xauthority
0     0  7601  7365  15   0 11320 5528 -      S    pts/1      0:00 emacs -nw

Many more features to `ps`

Note that ps causes the ``observer effect'' (observing the process table affects the process table, which is very true of top, especially if you set it to rapidly refresh)

Many more features to `ps`

Some favorite ps variations:

ps -ef(System V)
ps -elf (System V)
ps axuw | grep username (BSD)
ps alxwww (BSD)
ps alxwwwe (BSD, show environmental variables)

`ps` itself can also act a bit like `pstree`

$ ps f
  PID TTY      STAT   TIME COMMAND
21915 pts/1    Ss     0:00 bash
22976 pts/1    S+     0:05  \_ emacs -nw 05-rootadmins.tex
27844 pts/2    Ss     0:00      \_ /bin/bash --noediting -i
17182 pts/2    R+     0:00          \_ ps f
18985 pts/0    Ss     0:00 bash
19153 pts/0    S+     0:00  \_ ssh langley@diablo.cs.fsu.edu

Making `ps` ultra-flexible

If you need to tailor ps output to arbitrary columns, you can use the -o option to specify exactly which columns you would like to display, and -k option to specify order:

$ ps k pid o pid,comm
  PID COMMAND
18985 bash
19153 ssh
21915 bash
22976 emacs
24527 ps
27844 bash

Making `ps` ultra-flexible

$ ps k comm o pid,comm
  PID COMMAND
18985 bash
21915 bash
27844 bash
22976 emacs
24729 ps
19153 ssh

Other process viewing tools

top -- Dynamically shows processes, idle time, memory usage, and load averages
pstree -- Nice filter that shows family hierarchy of processes

`top` example

[root@smtpin MailScanner]# top -b -n 1
top - 07:09:25 up 42 days, 20:18,  2 users,  load average: 1.34, 1.56, 1.79
Tasks: 166 total,   1 running, 165 sleeping,   0 stopped,   0 zombie
Cpu(s): 12.7% us,  1.6% sy,  0.0% ni, 84.3% id,  1.3% wa,  0.0% hi,  0.0% si
Mem:   4149124k total,  3794188k used,   354936k free,   202476k buffers
Swap:  4192956k total,     4960k used,  4187996k free,  2677940k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 5675 root      15   0 68888  58m 2788 S    4  1.4   0:03.08 MailScanner
 5686 root      15   0  3520  900  676 R    2  0.0   0:00.01 top
26663 root      16   0 38616  29m 3464 S    2  0.7   0:29.90 MailScanner
    1 root      16   0  1980  548  468 S    0  0.0   0:45.81 init

`pstree` example

init-+-MailScanner
     |-MailScanner-+-16*[MailScanner]
     |             `-4*[MailScanner---MailScanner]
     +-acpid
     +-atd
     +-clamd
     +-crond
     +-cups-config-dae
     +-cupsd

Root root remedies for sluggish system

One process has been running for a long time and is 
accumulating a lot of processor time (for instance, top
shows it at the top of the list consistently) → typically,
this can be cleaned up by simply killing that one process. (If this is an
ordinary user process, this is
often the result of a controlling terminal having gone awry.)

Root remedies for sluggish system

Long-term Remedies
Involve more performance analysis (for instance, you might try the venerable SAR package to profile a Linux/Unix system; in the Windows world, Microsoft has LOGMAN and PAL)
More physical resources are inexpensive: may need more nodes, nodes may need faster CPU, more memory, better i/o

Root remedies for sluggish system

Finally: talk to people writing code; often small optimizations in database access, for instance, can have large performance gains

The future?

Permissions have not generally been enforced for privileged processes. However, with systems such as SeLinux and TOMOYO, we are now seeing enforcement of security policies even for privileged processes -- this can be disconcerting to system administrators who are used to privileged processes having free rein.

Root and Administrator Tasks: Process Management

Root and Administrator Tasks: Process Management

Root and Administrator Tasks: Process Management

Root and Administrator Tasks: Process Management

Root and Administrator Tasks: Process Management

Root and Administrator Tasks: Process Management

Root and Administrator Limitations: Process Management

Root and Administrator Limitations: Process Management

Root and Administrator Limitations: Process Management

How to become ``root''? Generally, people use something along the way of sudo, su, or login

How to become root? login, su, sudo

How to become root? login, su, sudo

How to become root? login, su, sudo

sudo: pseudo su, or how to set up safer su

sudo: pseudo su, or how to set up safer su

sudo: pseudo su, or how to set up safer su

sudo: pseudo su, or how to set up safer su

sudo: pseudo su, or how to set up safer su

System Load Average

System Load Average

Idle Time

Idle Time

Process Monitoring: ps

Process Monitoring: ps

Process Manipulation:

Example ps output from long, long ago

Example ps output from the more recent past

Example ps output from the more recent past

Many more features to ps

Many more features to ps

ps itself can also act a bit like pstree

Making ps ultra-flexible

Making ps ultra-flexible

Other process viewing tools

top example

pstree example

Root root remedies for sluggish system

Root remedies for sluggish system

Root remedies for sluggish system

The future?

How to become ``root''? Generally, people use something along the way of `sudo`, `su`, or `login`

How to become root? `login`, `su`, `sudo`

How to become root? `login`, `su`, `sudo`

How to become root? `login`, `su`, `sudo`

Process Monitoring: `ps`

Example `ps` output from long, long ago

Example `ps` output from the more recent past

Example `ps` output from the more recent past

Many more features to `ps`

Many more features to `ps`

`ps` itself can also act a bit like `pstree`

Making `ps` ultra-flexible

Making `ps` ultra-flexible

`top` example

`pstree` example