0x324 Linux Admin
- 1. Service Management
- 2. Network Management
- 3. Package Management
- 4. File System Management
- 5. Utilities
- 6. Credentials
- 7. Terminal
- 8. Reference
1. Service Management
The initialization daemon is the first process to be started by the kernel on the Linux server (with ppid 0 and pid 1). The original implementation was BSD init
and SysVinit
. Currently many linux distributions are adopting systemd
(e.g: Ubuntu, RHEL, Fedora distributions)
runlevel
is a categorization number that determines what services are started and what services are stopped.
2. Network Management
(sudo) netstat -tupln
see all listening tcp/udp pid programs
3. Package Management
3.1. Debian
3.2. Redhat
yum list available | grep postgres
: search available packages
4. File System Management
/proc/sys/fs/file-max
: file limit
/proc/sys/fs/file-nr
: currently opened files
5. Utilities
5.1. Awk
awk '!seen[$0]++' text
: remove duplicates from text
5.2. Others
shuf input.txt > output.txt
: shuffle lines of a given file
6. Credentials
6.1. Users / Groups
File (/etc/passwd) nonsensitive system password file
- login name: unique user name encrypted password: DES hash of password, x if shadow password enabled
- User ID (UID): superuser (root) if value 0
- Group ID (GID): group id of the first group
- Comment: text about the user
- home directory: HOME variable
- login shell: shell
File (/etc/shadow) sensitive password file. password hash is saved here
File (/etc/group) group info (note that part of the info is saved in /etc/passwd) . current login user's group can be checked with group (1)
- group name: unique group name
- encrypted password: group password, x if shadow password enabled
- group ID (GID): group id
- user list: users
7. Terminal
stty -a: show terminal line settings
8. Reference
[1] Linux Bible