Time synchronization is the process of keeping the system clock accurate and consistent across every machine in a network. On a single laptop, a few seconds of drift is an annoyance. On a server, it is a correctness problem. Authentication protocols reject tickets that are outside a narrow time window, log entries from different hosts…
Samba permissions are enforced at two layers that must both allow an operation. The first layer is the Samba configuration in smb.conf: the valid users, write list, and read only parameters determine who can connect to the share and what they can do. The second layer is the Linux filesystem permissions on the actual directory…
Samba is the Linux implementation of the SMB/CIFS protocol, the file-sharing protocol that Windows clients use. The previous chapter covered NFS, which shares files between Unix-like systems; Samba shares files with Windows, macOS, and Linux clients that speak the SMB protocol. The LFCE exam objectives include providing SMB/CIFS shares to clients using Samba . The…
The previous chapter configured a basic NFS export. This chapter covers the options that control who can access the share, what they can do with it, and how the server maps their identity. The /etc/exports syntax is deceptively simple, and a single space in the wrong place changes the meaning of the line. The security…
NFS (Network File System) is the standard protocol for sharing directories across a Unix-like network. The server exports a directory from its local filesystem, and clients mount it over the network as if it were a local filesystem. The previous chapters covered web servers and mail servers, both of which provide application-level services; NFS provides…
Every command in Bash returns a number between 0 and 255 when it finishes. That number is the exit status, and it is the mechanism by which commands, functions, and scripts communicate success or failure to their caller. The previous chapter covered functions and the return command; this chapter covers the exit status in detail:…
A function is a named block of commands that can be called repeatedly. In Bash, a function is not a separate program; it is a set of commands stored in the current shell’s memory and executed when the function name is invoked. The previous chapters covered loops and arrays; this chapter covers the construct that…
An associative array is a variable that maps string keys to string values. It is the Bash equivalent of a dictionary or hash table, and it is available natively in Bash version 4 and later . The previous chapter covered indexed arrays, which use numeric subscripts; this chapter covers the associative form, where the subscript…
An indexed array is a variable that holds multiple values under a single name. Each value is accessed by a numeric index, and the indices are not required to be contiguous. Bash arrays are not a separate type; they are a Bash feature that extends the variable syntax with subscripts. The previous chapters covered scalars…
A while loop repeats a command list as long as a condition is true. An until loop repeats it as long as a condition is false. The two constructs are mirror images: while runs while the condition succeeds, and until runs while the condition fails. Both evaluate the condition before every iteration, so a loop…